ci: warm-cache run without precompiled headers

Clang rebuilds the precompiled header with a fresh timestamp on every
run, so every file that includes it misses the cache: the warm run hit
178 of 927 compiles on Linux. Forward ORCA_EXTRA_BUILD_ARGS from the
macOS and Windows build scripts the way build_linux.sh already does, and
pass SLIC3R_PCH=OFF through it whenever ccache is enabled.

.github/workflows/build_orca.yml

@@ -76,6 +76,37 @@ jobs:
           if (-not (Test-Path "$cmakeBin\cmake.exe")) { throw "cmake.exe not found at $cmakeBin" }
           Add-Content -Path $env:GITHUB_PATH -Value $cmakeBin
 
+      # Compiler cache. Objects are keyed on the preprocessed source, the
+      # compiler binary and the flags, so a leg only ever hits its own entries.
+      # Pushes save (main keeps the cache warm); pull requests restore it and
+      # discard what they compiled, so the store does not grow per PR. A failed
+      # install only costs the caching, not the build.
+      - name: Compiler cache
+        id: ccache
+        if: ${{ !inputs.macos-combine-only }}
+        continue-on-error: true
+        uses: hendrikmuhs/ccache-action@v1.2
+        with:
+          key: ${{ runner.os }}-${{ inputs.arch || 'amd64' }}${{ runner.os == 'Windows' && format('-{0}', inputs.compiler) || '' }}
+          max-size: 2G
+          # TEST: pull requests save too, so a second run on this branch measures
+          # a warm cache. Restore-only for pull_request before merge.
+          save: true
+
+      - name: Enable compiler cache
+        if: ${{ steps.ccache.outcome == 'success' }}
+        shell: bash
+        run: |
+          echo "CMAKE_C_COMPILER_LAUNCHER=ccache" >> "$GITHUB_ENV"
+          echo "CMAKE_CXX_COMPILER_LAUNCHER=ccache" >> "$GITHUB_ENV"
+          # Needed for precompiled headers and for headers a fresh checkout
+          # has just written.
+          echo "CCACHE_SLOPPINESS=pch_defines,time_macros,include_file_mtime,include_file_ctime" >> "$GITHUB_ENV"
+          # Clang rebuilds the precompiled header with a fresh timestamp on
+          # every run, so every file that includes it misses the cache. All
+          # three build scripts forward this to the slicer configure.
+          echo "ORCA_EXTRA_BUILD_ARGS=-DSLIC3R_PCH=OFF" >> "$GITHUB_ENV"
+
       - name: Get the version and date on Ubuntu and macOS
         if: runner.os != 'Windows'
         run: |
@@ -670,3 +701,8 @@ jobs:
           asset_name: orca_custom_preset_tests.zip
           asset_content_type: application/octet-stream
           max_releases: 1
+
+      - name: Compiler cache statistics
+        if: ${{ always() && steps.ccache.outcome == 'success' }}
+        shell: bash
+        run: ccache -s -v || ccache -s

build_release_macos.sh

@@ -255,6 +255,7 @@ function build_slicer() {
             mkdir -p "$PROJECT_BUILD_DIR"
             cd "$PROJECT_BUILD_DIR"
             if [ "1." != "$BUILD_ONLY". ]; then
+                read -r -a EXTRA_BUILD_ARGS <<< "${ORCA_EXTRA_BUILD_ARGS:-}"
                 cmake "${PROJECT_DIR}" \
                     -G "${SLICER_CMAKE_GENERATOR}" \
                     -DORCA_TOOLS=ON \
@@ -264,7 +265,8 @@ function build_slicer() {
                     -DCMAKE_OSX_ARCHITECTURES="${_ARCH}" \
                     -DCMAKE_OSX_DEPLOYMENT_TARGET="${OSX_DEPLOYMENT_TARGET}" \
                     -DCMAKE_IGNORE_PREFIX_PATH="${CMAKE_IGNORE_PREFIX_PATH}" \
-                    ${CMAKE_POLICY_COMPAT}
+                    ${CMAKE_POLICY_COMPAT} \
+                    "${EXTRA_BUILD_ARGS[@]}"
             fi
             cmake --build . --config "$BUILD_CONFIG" --target "$SLICER_BUILD_TARGET"
         )

build_release_vs.bat

@@ -164,10 +164,10 @@ cd %build_dir%
 echo on
 set CMAKE_POLICY_VERSION_MINIMUM=3.5
 if "%USE_NINJA%"=="1" (
-    cmake .. -G %CMAKE_GENERATOR% %CLANG_ARG% -DORCA_TOOLS=ON %SIG_FLAG% -DBUILD_TESTS=%BUILD_TESTS% -DCMAKE_BUILD_TYPE=%build_type%
+    cmake .. -G %CMAKE_GENERATOR% %CLANG_ARG% -DORCA_TOOLS=ON %SIG_FLAG% -DBUILD_TESTS=%BUILD_TESTS% -DCMAKE_BUILD_TYPE=%build_type% %ORCA_EXTRA_BUILD_ARGS%
     cmake --build . --config %build_type% --target all
 ) else (
-    cmake .. -G %CMAKE_GENERATOR% -A %arch% %TOOLSET_ARG% -DORCA_TOOLS=ON %SIG_FLAG% -DBUILD_TESTS=%BUILD_TESTS% -DCMAKE_BUILD_TYPE=%build_type%
+    cmake .. -G %CMAKE_GENERATOR% -A %arch% %TOOLSET_ARG% -DORCA_TOOLS=ON %SIG_FLAG% -DBUILD_TESTS=%BUILD_TESTS% -DCMAKE_BUILD_TYPE=%build_type% %ORCA_EXTRA_BUILD_ARGS%
     cmake --build . --config %build_type% --target ALL_BUILD -- -m
 )
 @echo off