to tune for more advanced processors while still supporting the minimum
processor in an architecture. We can do this with the '-mtune=' option
to gcc for alpha, sparc64, and powerpc and with the mis-named '-mcpu='
option for i386.
This defaults to tuning i386 builds for i686 machines though not using
any instructions that aren't found on an 80386. For alpha it defaults
to tuning for an EV5.
Approved by: peter
Peril sensitive sunglasses borrowed from: peter
8605c6b2ad