[GOOGLE] Back port discriminator patches to gcc-4_8

[Cary Coutant]

> The warning was attributed to the wrong lineno. Looks like
> discriminator does not work well when it coexists with macros.

I think warn_uninit in tree-ssa.c needs one of these:

  location = map_discriminator_location (location);

There may still be other places where calls to
linemap_resolve_location have been added since this patch was
originally developed.

-cary