feat: disable ccache by default, enable with --use-ccache flag

This change modifies the LLVM build process to disable ccache by default
and only enable it when the --use-ccache flag is explicitly passed. This
reduces CI storage consumption while still allowing developers to opt-in
to ccache for faster incremental builds.

Changes:
- Modified build_llvm() to accept use_ccache parameter (defaults to False)
- Updated ccache logic to only enable when use_ccache=True and platform is not Windows
- Pass options.use_ccache from main() to build_llvm() call

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

build-scripts/build_llvm.py

@@ -48,7 +48,7 @@ def query_llvm_version(llvm_info):
     return response['sha']
 
 
-def build_llvm(llvm_dir, platform, backends, projects, use_clang=False, extra_flags=''):
+def build_llvm(llvm_dir, platform, backends, projects, use_clang=False, extra_flags='', use_ccache=False):
     LLVM_COMPILE_OPTIONS = [
         '-DCMAKE_BUILD_TYPE:STRING="Release"',
         "-DCMAKE_EXPORT_COMPILE_COMMANDS=ON",
@@ -68,8 +68,8 @@ def build_llvm(llvm_dir, platform, backends, projects, use_clang=False, extra_fl
         "-DLLVM_OPTIMIZED_TABLEGEN:BOOL=ON",
     ]
 
-    # ccache is not available on Windows
-    if not "windows" == platform:
+    # ccache is opt-in via --use-ccache flag
+    if not "windows" == platform and use_ccache:
         LLVM_COMPILE_OPTIONS.append("-DLLVM_CCACHE_BUILD:BOOL=ON")
     # perf support is available on Linux only
     if "linux" == platform:
@@ -339,7 +339,7 @@ def main():
         if (
             build_llvm(
                 llvm_dir, platform, options.arch, options.project, options.use_clang,
-                options.extra_cmake_flags
+                options.extra_cmake_flags, options.use_ccache
             )
             is not None
         ):