`--ffile-prefix-map` instead of `--fdebug-prefix-map` for deterministic builds

[tbarrella]

Hello, I found that using --ffile-prefix-map here fixed non-deterministic GoLink output for a build.

See here; this is a newer flag that also handles absolute paths from __FILE__ macros.

Would it be safe to update rules_go to use the newer flag?

[fmeum]

I would think so at this point. @dzbarsky @keith do you happen to know how widely supported that flag is among compilers?

[keith]

based on that site it was added:

-ffile-prefix-map=OLD=NEW is an alias for both -fdebug-prefix-map and -fmacro-prefix-map. (available since GCC 8 and Clang 10)

for newer clangs it's actually nicer to do -ffile-compilation-dir=. so you don't have to come up with the non-hermetic OLD path. but i don't think that one made its way to gcc.

not sure how msvc factors in here

[dzbarsky]

We could gate the behavior based on @rules_cc//cc/compiler :) I think using better flags when possible makes a lot of sense