feat: add --use-ccache CLI argument to build_llvm.py

Add a new --use-ccache flag that will allow developers to opt-in to using
ccache for LLVM builds. This is part of a larger effort to disable ccache
by default to reduce CI storage consumption while still allowing local
developers to benefit from faster incremental builds.

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

Author: lum1n0us

build-scripts/build_llvm.py

@@ -270,6 +270,11 @@ def main():
         action="store_true",
         help="use clang instead of gcc",
     )
+    parser.add_argument(
+        "--use-ccache",
+        action="store_true",
+        help="enable ccache for faster incremental LLVM builds (disabled by default to reduce CI storage consumption, recommended for local development)",
+    )
     parser.add_argument(
         "--extra-cmake-flags",
         type=str,