Intel macOS: use Mozilla-bootstrapped clang instead of Homebrew llvm@19

Co-authored-by: Xmader <16057139+Xmader@users.noreply.github.com>

Author: Copilot

.github/workflows/test-and-publish.yaml

@@ -260,8 +260,10 @@ jobs:
             # to llvm@19: the unversioned `llvm` formula (currently 23.x)
             # has no bottle for Intel macOS or macOS 14, so it silently
             # falls back to a multi-hour from-source build here.
-            brew install llvm@19
-            echo "PATH=$(brew --prefix llvm@19)/bin:$PATH" >> $GITHUB_ENV
+            if [[ "$(uname -m)" != "x86_64" ]]; then # no llvm@19 bottle for Intel macOS; use Xcode's clang there
+              brew install llvm@19
+              echo "PATH=$(brew --prefix llvm@19)/bin:$PATH" >> $GITHUB_ENV
+            fi
           fi
           echo "Installing python deps"
           poetry self add "poetry-dynamic-versioning[plugin]"

setup.sh

@@ -28,8 +28,15 @@ elif [[ "$OSTYPE" == "darwin"* ]]; then # macOS
   # `llvm`/`lld` have no bottles for Intel macOS or macOS 14 and build from
   # source for hours (and lld pulls in the unversioned llvm). Both kegs are
   # keg-only, so put them on PATH explicitly.
-  brew install llvm@19 lld@19
-  export PATH="$(brew --prefix llvm@19)/bin:$(brew --prefix lld@19)/bin:$PATH"
+  if [[ "$(uname -m)" == "x86_64" ]]; then
+    # Homebrew no longer ships llvm@19/lld@19 bottles for Intel macOS and would
+    # build LLVM from source (which fails), so use the clang toolchain that
+    # Mozilla's own bootstrap downloads once the source is extracted (below).
+    echo "Intel macOS: will use Mozilla's bootstrapped clang"
+  else
+    brew install llvm@19 lld@19
+    export PATH="$(brew --prefix llvm@19)/bin:$(brew --prefix lld@19)/bin:$PATH"
+  fi
 elif [[ "$OSTYPE" == "msys"* || "$OSTYPE" == "cygwin"* ]]; then # Windows
   echo "Dependencies are not going to be installed automatically on Windows."
 else
@@ -87,6 +94,12 @@ echo "Done downloading spidermonkey source code"
 echo "Building spidermonkey"
 cd firefox-source
 
+if [[ "$OSTYPE" == "darwin"* && "$(uname -m)" == "x86_64" ]]; then
+  # Fetch Mozilla's prebuilt clang (>= 19) for Intel macOS, see above
+  python3 ./mach --no-interactive bootstrap --application-choice=js --no-system-changes
+  export PATH="$HOME/.mozbuild/clang/bin:$PATH"
+fi
+
 # Apply patching
 # making it work for both GNU and BSD (macOS) versions of sed
 sed -i'' -e 's/os not in ("WINNT", "OSX", "Android")/os not in ("WINNT", "Android")/' ./build/moz.configure/pkg.configure # use pkg-config on macOS