Heads-up: Simplify Mk/bsd.gcc.mk (PR244008)

[Gerald Pfeifer]

Hi folks,

I just submitted a larger update to Mk/bsd.gcc.mk for an exp-run:

  https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=244008

This _should_ be platform agnostic and in fact not materially change 
anything (in particular in clean build environments).

I still wanted to give you a heads-up, in particular since powerpc* 
is the only significant user of USE_GCC=any (where it's not synonymous 
with USE_GCC=yes).

Gerald