cmake : add PCH and unity build to improve build times (#28091)

* scripts : add initial profiling script (wip)

* src : add precompile headers (PCH) for models.h

* common : add common.h as PCH

* ggml : add PCH for ggml-impl.h

* mtmd : use PCH for models.h

* scripts : add script to build with Server/Tools/Tests

* server : add PCH for common.h

* docs: add profiling progress notes (wip)

* ggml : add exclude for GCC + SVE on ARM

Refs: https://github.com/ggml-org/llama.cpp/actions/runs/33393906061/job/99493756214?pr=28091

* ggml : attempt to fix use of std::hardware_destructive_inference_size

Refs: https://github.com/ggml-org/llama.cpp/actions/runs/33396221677/job/99501265689?pr=28091

* squash! ggml : attempt to fix use of std::hardware_destructive_inference_size

Add a version check for GCC 12 to conditionally apply the `-Winterference-size`
pragma.

* editorconfig : exclude profiling reports dir

This directory will not be included in the merge later and this commit
can be ignore at that point. Just fixing to keep CI happy.

* ggml : skip PCH for gcc on non-x86 architectures

* tests : add PCH for peg-parser/tests.h

There are 7 peg-parser tests that can share one PCH instead of then each
parsing the full tests.h.

* common : add PCH for chat.h

* docs : update linux build profiling full results

Just updating after a number of PCH additions. These are not exact
figures and will vary a bit from run to run, but they give a general idea
of the performance impact of PCH.

* cmake : introduce unity build for models

This commit introduces a unity build for the models to improve
compilation time.

The improvements were roughly the following:
```console
+------------------------+-----+------------+------------+------------+
| Build                  | TUs | Frontend   | Backend    | Total      |
+------------------------+-----+------------+------------+------------+
| Full,    master        | 396 |   811.0 s  |   692.2 s  | 1,503.2 s  |
| Full,    with PCH      | 405 |   380.0 s  |   664.7 s  | 1,044.7 s  |
| Full,    with PCH + UB | 264 |   357.7 s  |   635.7 s  |   993.4 s  |
+------------------------+-----+------------+------------+------------+

TU   = Translation Unit.
Full = includes Server, Tools, and Tests.
PCH  = precompiled headers.
UB   = unity build for models.
```

* docs : update linux profiling table with unitiy build results

* docs : update mac profiling results to include unity build [no ci]

* docs: remove profiling reports

* scripts : merge build profile scripts into one script

I was lazy before and just copied the first script to enable Tests,
Server, and Tools. This now merges them into a single script.

* Revert "editorconfig : exclude profiling reports dir" [no ci]

This reverts commit 2922a12118.

* src : rename ggml_view_2d_slice to gemma3n_view_2d_slice

This is to be consistent with the rename in gemma4.cpp which was
required to avoid a name clash.

* cmake : add build profile script for windows [no ci]

This commit adds a port of the scripts/build-profile.sh script to
windows powershell.

This was developed on Windows on ARM but should work on X64 as well but
needs to be tested there as well.

scripts/build-profile.ps1

@@ -0,0 +1,136 @@
+# Compile-time profiling using clang -ftime-trace + ClangBuildAnalyzer.
+#
+# Usage:
+#   .\scripts\build-profile.ps1 [-Full] [-Jobs N]
+#
+# -Full : include Server, Tools, and Tests (default: minimal build)
+# -Jobs :  number of parallel jobs (default: all cores)
+#
+# Requires ClangBuildAnalyzer:
+#   https://github.com/aras-p/ClangBuildAnalyzer
+
+param(
+    [switch]$Full,
+    [int]$Jobs = [Environment]::ProcessorCount
+)
+
+$ErrorActionPreference = "Stop"
+
+$ScriptDir = Split-Path -Parent $MyInvocation.MyCommand.Path
+$RootDir = Split-Path -Parent $ScriptDir
+
+if ($Full) {
+    $BuildDir = Join-Path $RootDir "build-profile-full"
+    $Report = Join-Path $BuildDir "profile-report-full.txt"
+} else {
+    $BuildDir = Join-Path $RootDir "build-profile-baseline"
+    $Report = Join-Path $BuildDir "profile-report.txt"
+}
+
+$OutputBin = Join-Path $BuildDir "clang_analysis.bin"
+
+if (-not (Get-Command clang++ -ErrorAction SilentlyContinue)) {
+    Write-Error "clang++ not found"
+    exit 1
+}
+
+if (-not (Get-Command ninja -ErrorAction SilentlyContinue)) {
+    Write-Error "ninja not found (required so cmake does not fall back to the Visual Studio/MSVC generator)"
+    exit 1
+}
+
+if (-not (Get-Command ClangBuildAnalyzer -ErrorAction SilentlyContinue)) {
+    Write-Error "ClangBuildAnalyzer not found`n  https://github.com/aras-p/ClangBuildAnalyzer/releases"
+    exit 1
+}
+
+$ClangVer = (clang++ --version | Select-Object -First 1)
+Write-Host "compiler : $ClangVer"
+Write-Host "build dir: $BuildDir"
+Write-Host "output   : $OutputBin"
+Write-Host "jobs     : $Jobs"
+Write-Host ""
+
+if (Get-Command ccache -ErrorAction SilentlyContinue) {
+    Write-Host "clearing ccache..."
+    ccache -C -z
+}
+
+$env:CCACHE_DISABLE = "1"
+
+$TestsFlag = if ($Full) { "ON" } else { "OFF" }
+$ToolsFlag = if ($Full) { "ON" } else { "OFF" }
+$ServerFlag = if ($Full) { "ON" } else { "OFF" }
+
+cmake --fresh `
+    -S $RootDir `
+    -B $BuildDir `
+    -G "Ninja" `
+    -DCMAKE_BUILD_TYPE=Release `
+    -DCMAKE_C_COMPILER=clang `
+    -DCMAKE_CXX_COMPILER=clang++ `
+    -DCMAKE_C_FLAGS="-ftime-trace" `
+    -DCMAKE_CXX_FLAGS="-ftime-trace" `
+    -DGGML_CCACHE=OFF `
+    -DGGML_OPENMP=ON `
+    -DGGML_NATIVE=OFF `
+    "-DLLAMA_BUILD_TESTS=$TestsFlag" `
+    -DLLAMA_BUILD_EXAMPLES=OFF `
+    "-DLLAMA_BUILD_TOOLS=$ToolsFlag" `
+    "-DLLAMA_BUILD_SERVER=$ServerFlag" `
+    -DLLAMA_BUILD_APP=OFF
+
+if ($LASTEXITCODE -ne 0) { exit $LASTEXITCODE }
+
+$StrayTrace = Join-Path $RootDir "-.json"
+if (Test-Path $StrayTrace) {
+    Remove-Item $StrayTrace -Force
+}
+
+Write-Host ""
+Write-Host "Initializing ClangBuildAnalyzer..."
+ClangBuildAnalyzer --start $BuildDir
+Write-Host ""
+
+Write-Host "building..."
+Write-Host ""
+
+$StartTime = Get-Date
+
+cmake --build $BuildDir --clean-first -j $Jobs
+
+if ($LASTEXITCODE -ne 0) { exit $LASTEXITCODE }
+
+$Elapsed = (Get-Date) - $StartTime
+
+Write-Host ""
+Write-Host ("build time: {0}s ({1}m {2}s)" -f [int]$Elapsed.TotalSeconds, [int]$Elapsed.TotalMinutes, $Elapsed.Seconds)
+Write-Host ""
+
+Write-Host "Aggregating profile metrics..."
+ClangBuildAnalyzer --stop $BuildDir $OutputBin | Out-Null
+
+Write-Host ""
+Write-Host ("=" * 80)
+
+$TUs = "?"
+if (Test-Path $Report) {
+    $Match = Select-String -Path $Report -Pattern "Compilation \((\d+)" | Select-Object -First 1
+    if ($Match) { $TUs = $Match.Matches[0].Groups[1].Value }
+}
+
+ClangBuildAnalyzer --analyze $OutputBin | Tee-Object -FilePath $Report
+
+Write-Host ""
+Write-Host "translation units: $TUs"
+Write-Host ""
+Write-Host "largest trace files (top 20 by size):"
+
+Get-ChildItem -Path $BuildDir -Recurse -Filter "*.json" |
+    Where-Object { $_.Name -ne "compile_commands.json" } |
+    Sort-Object Length -Descending |
+    Select-Object -First 20 |
+    ForEach-Object { "{0,8:F1} KB  {1}" -f ($_.Length / 1024), $_.FullName }
+
+Write-Host ""
+Write-Host "ClangBuildAnalyzer report was generated: $Report"

scripts/build-profile.sh

@@ -0,0 +1,122 @@
+#!/usr/bin/env bash
+# Compile-time profiling using clang -ftime-trace + ClangBuildAnalyzer.
+#
+# Usage:
+#   ./scripts/build-profile.sh [--full] [-jN]
+#
+# --full: include Server, Tools, and Tests (default: minimal build)
+# -jN   :  number of parallel jobs (default: all cores)
+#
+# Requires ClangBuildAnalyzer:
+#   macOS: brew install clang-build-analyzer
+#   Linux: https://github.com/aras-p/ClangBuildAnalyzer.git
+
+set -euo pipefail
+
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+ROOT_DIR="$(cd "${SCRIPT_DIR}/.." && pwd)"
+
+FULL=0
+JOBS="-j$(nproc 2>/dev/null || sysctl -n hw.ncpu)"
+
+for arg in "$@"; do
+    case "${arg}" in
+        --full) FULL=1 ;;
+        -j*)    JOBS="${arg}" ;;
+        *) echo "error: unknown argument: ${arg}" >&2; exit 1 ;;
+    esac
+done
+
+if [ "${FULL}" -eq 1 ]; then
+    BUILD_DIR="${ROOT_DIR}/build-profile-full"
+    REPORT="${BUILD_DIR}/profile-report-full.txt"
+else
+    BUILD_DIR="${ROOT_DIR}/build-profile-baseline"
+    REPORT="${BUILD_DIR}/profile-report.txt"
+fi
+
+OUTPUT_BIN="${BUILD_DIR}/clang_analysis.bin"
+
+if ! command -v clang++ &>/dev/null; then
+    echo "error: clang++ not found" >&2
+    exit 1
+fi
+
+if ! command -v ClangBuildAnalyzer &>/dev/null; then
+    echo "error: ClangBuildAnalyzer not found" >&2
+    echo "  brew install clangbuildanalyzer  (macOS)" >&2
+    echo "  or: https://github.com/aras-p/ClangBuildAnalyzer/releases" >&2
+    exit 1
+fi
+
+CLANG_VER=$(clang++ --version | head -1)
+echo "compiler : ${CLANG_VER}"
+echo "build dir: ${BUILD_DIR}"
+echo "output   : ${OUTPUT_BIN}"
+echo "jobs     : ${JOBS}"
+echo
+
+if command -v ccache &>/dev/null; then
+    echo "clearing ccache..."
+    ccache -C -z
+fi
+
+export CCACHE_DISABLE=1
+
+cmake --fresh \
+    -S "${ROOT_DIR}" \
+    -B "${BUILD_DIR}" \
+    -DCMAKE_BUILD_TYPE=Release \
+    -DCMAKE_C_COMPILER=clang \
+    -DCMAKE_CXX_COMPILER=clang++ \
+    -DCMAKE_C_FLAGS="-ftime-trace" \
+    -DCMAKE_CXX_FLAGS="-ftime-trace" \
+    -DGGML_CCACHE=OFF \
+    -DGGML_OPENMP=ON \
+    -DGGML_NATIVE=OFF \
+    -DLLAMA_BUILD_TESTS=$([ "${FULL}" -eq 1 ] && echo ON || echo OFF) \
+    -DLLAMA_BUILD_EXAMPLES=OFF \
+    -DLLAMA_BUILD_TOOLS=$([ "${FULL}" -eq 1 ] && echo ON || echo OFF) \
+    -DLLAMA_BUILD_SERVER=$([ "${FULL}" -eq 1 ] && echo ON || echo OFF) \
+    -DLLAMA_BUILD_APP=OFF
+
+echo
+
+echo "Initializing ClangBuildAnalyzer..."
+ClangBuildAnalyzer --start "${BUILD_DIR}"
+echo
+
+echo "building..."
+echo
+
+START=$(date +%s)
+
+cmake --build "${BUILD_DIR}" --clean-first "${JOBS}"
+
+END=$(date +%s)
+ELAPSED=$((END - START))
+
+echo
+printf "build time: %ds (%dm %ds)\n" "${ELAPSED}" "$((ELAPSED / 60))" "$((ELAPSED % 60))"
+echo
+
+echo "Aggregating profile metrics..."
+ClangBuildAnalyzer --stop "${BUILD_DIR}" "${OUTPUT_BIN}" > /dev/null
+
+echo
+echo "================================================================================"
+TUS=$(grep -oP "Compilation \(\K[0-9]+" "${REPORT}" 2>/dev/null || echo "?")
+ClangBuildAnalyzer --analyze "${OUTPUT_BIN}" | tee "${REPORT}"
+
+echo
+echo "translation units: ${TUS}"
+echo
+echo "largest trace files (top 20 by size):"
+find "${BUILD_DIR}" -name "*.json" ! -name "compile_commands.json" \
+    | xargs ls -l 2>/dev/null \
+    | awk 'NF>5 {print $5, $NF}' \
+    | sort -rn \
+    | awk 'NR<=20 {printf "%8.1f KB  %s\n", $1/1024, $2}'
+
+echo
+echo "ClangBuildAnalyzer report was generated: ${REPORT}"