Add GLOBAL_CLANG_EXTERNAL_CFLAGS_NO_OVERRIDE to third-party code

Bug: http://b/215753485

This allows enabling a new warning from the compiler update for
first-party code.  This is less precise than the check in build/soong
(also overrides for vendor/google, for e.g.) because of being written in
Make.

Test: With new clang, verify the following:
    lunch oriole;
    m out/target/product/oriole/obj_arm/SHARED_LIBRARIES/libexynosdisplay_intermediates/libresource/ExynosMPP.o
Change-Id: I13080fec71e282c4b528a6d01b967b1c0c4aef02