COMPILER

So COMPILER changed again, hopefully for the last time.

It's now definitely a list that's somewhat more specific
base-gcc
base-clang
gcc3 (for really old stuff
ports-gcc
ports-clang

'gcc' and 'clang' are currently shortcuts so that the existing stuff
doesn't change too much.

this went thru a bulk. And is documented in bsd.port.mk(5)

mostly because people whined they didn't understand things. Hopefully
this will make sense for everyone.

This is needed for limber stuff like gcc-only, which didn't make
enough sense...

COMPILER=base-gcc gcc3 ports-gcc

(for stuff that's happy with any gcc)

vs.

COMPILER=ports-gcc

(for stuff that really wants the gcc 4.9 from ports)