message: Use -fmerge-all-constants with clang.
  The code base still has memory access bugs that go away when we use
  fmerge-all-constants.
diff: @@ -353,7 +353,10 @@ def _features(cpu, compiler, ctx):
  flag_set(
  actions = all_cpp_compile_actions(),
  flag_groups = [
  - flag_group(flags = ["-fexperimental-new-pass-manager"]),
  + flag_group(flags = [
  + "-fexperimental-new-pass-manager",
  + "-fmerge-all-constants",
  + ]),
  ] if compiler == "clang" else [],
  ),
  flag_set(
  