Disable "taking address of packed member" clang warning.

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 ffe3ac860cbfddcd3da0c1eac3404dbae06f8268..c92e17fa4b01b01db6ba8aeb15669fc5ecaf13e5 100644
--- a/build/config/compiler/BUILD.gn
+++ b/build/config/compiler/BUILD.gn
@@ -1008,6 +1008,13 @@ config("default_warnings") {
         # TODO(thakis): https://crbug.com/604888
         "-Wno-undefined-var-template",
       ]
+
+      if (llvm_force_head_revision) {
+        cflags += [
+          # TODO(eugenis): Clean up, http://crbug.com/619640
+          "-Wno-address-of-packed-member",
+        ]
+      }
     }
   }
 }