clang: Disable new warning -Wbitfield-width on the ToT bots.

build/config/compiler/BUILD.gn

Index: build/config/compiler/BUILD.gn
diff --git a/build/config/compiler/BUILD.gn b/build/config/compiler/BUILD.gn
index 1a7df3025fa011bbc8e1c257f3169229c99594ae..00b79bfb0afe212e912874cbc26233188895f8e8 100644
--- a/build/config/compiler/BUILD.gn
+++ b/build/config/compiler/BUILD.gn
@@ -1047,6 +1047,17 @@ if (is_clang) {
       "-Wno-shift-negative-value",
     ]
   }
+
+  if (exec_script("//tools/clang/scripts/update.py",
+                  [ "--print-revision" ],
+                  "trim string") != "245965-1") {
+    default_warning_flags += [
+      # TODO(thakis): Move this into outer if once clang is rolled far enough
+      # that the pinned clang understands this flag.
+      # TODO(thakis): Consider enabling this?
+      "-Wno-bitfield-width",
+    ]
+  }
 }
 
 # chromium_code ---------------------------------------------------------------