fix(CI): switch to an older Xcode version

Author: Xmader

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

@@ -124,6 +124,10 @@ jobs:
         if: ${{ !startsWith(matrix.os, 'ubuntu') && steps.cache-spidermonkey.outputs.cache-hit != 'true' }}
         with:
           python-version: ${{ matrix.python_version }}
+      - name: Setup XCode
+        if: ${{ matrix.os == 'macos-15-intel' && steps.cache-spidermonkey.outputs.cache-hit != 'true' }}
+        # Xcode 16.x removed the old linker behaviour (-ld64 or -ld_classic) that SpiderMonkey relies on, so we need to switch to an older version
+        run: sudo xcode-select -switch /Applications/Xcode_16.0.app
       - name: Build spidermonkey
         if: ${{ steps.cache-spidermonkey.outputs.cache-hit != 'true' }}
         run: ./setup.sh

setup.sh

@@ -63,7 +63,7 @@ sed -i'' -e 's/return JS::GetWeakRefsEnabled() == JS::WeakRefSpecifier::Disabled
 sed -i'' -e 's/return !IsIteratorHelpersEnabled()/return false/' ./js/src/vm/GlobalObject.cpp # forcibly enable iterator helpers
 sed -i'' -e '/MOZ_CRASH_UNSAFE_PRINTF/,/__PRETTY_FUNCTION__);/d' ./mfbt/LinkedList.h # would crash in Debug Build: in `~LinkedList()` it should have removed all this list's elements before the list's destruction
 sed -i'' -e '/MOZ_ASSERT(stackRootPtr == nullptr);/d' ./js/src/vm/JSContext.cpp # would assert false in Debug Build since we extensively use `new JS::Rooted`
-sed -i'' -e 's/"-fuse-ld=ld"/"-Wl,-ld_classic" if c_compiler.version > "14.0.0" else "-fuse-ld=ld"/' ./build/moz.configure/toolchain.configure # XCode 15 changed the linker behaviour. See https://developer.apple.com/documentation/xcode-release-notes/xcode-15-release-notes#Linking
+sed -i'' -e 's/"-fuse-ld=ld"/"-ld64" if c_compiler.version > "14.0.0" else "-fuse-ld=ld"/' ./build/moz.configure/toolchain.configure # XCode 15 changed the linker behaviour. See https://developer.apple.com/documentation/xcode-release-notes/xcode-15-release-notes#Linking
 sed -i'' -e 's/defined(XP_WIN)/defined(_WIN32)/' ./mozglue/baseprofiler/public/BaseProfilerUtils.h # this header file is introduced to js/Debug.h in https://phabricator.services.mozilla.com/D221102, but it would be compiled without XP_WIN in this building configuration
 
 cd js/src