This will port the following from V8's old Makefile:
https://cs.chromium.org/chromium/src/v8/Makefile?q=ggdb3+file:%5Esrc/&sq=package:chromium&l=95&dr=C

There doesn't seem to be a way to bypass any cflags in gn. So we need to add this to V8's toolchain guarded by a gn arg.

See also:
https://groups.google.com/forum/#!topic/v8-dev/zouCvRnKw8A