clang build.py: try to spell llvm_force_head_revision correctly

Bug: 958978, 884608
Change-Id: I073cd73e1b2c17f609978199b1e4e95bc1c98085
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1594580
Commit-Queue: Hans Wennborg <hans@chromium.org>
Auto-Submit: Hans Wennborg <hans@chromium.org>
Reviewed-by: Nico Weber <thakis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#656350}

tools/clang/scripts/build.py

@@ -768,7 +768,7 @@ def main():
                fuchsia_lib_dst_dir)
 
   # Run tests.
-  if args.run_tests or args.force_head_revision:
+  if args.run_tests or args.llvm_force_head_revision:
     os.chdir(LLVM_BUILD_DIR)
     RunCommand(['ninja', 'cr-check-all'], msvc_arch='x64')
   if args.run_tests: