This separates the "PPro/Celeron/Pentium-II" compile option into "PPro"
and "Pentium-II/Celeron" options.

This allows us to explicitly support the Pentium II and Celeron,
specifically adding the `-march' option for the chip and enabling the
unaligned copy optimizations.  PPro support remains unchanged.

This patch is by Luuk van der Duim with some changes by me (primarily to
also support the pre-Coppermine Celeron chips, since those use Pentium
II cores).  This patch has been in 2.5-mm for awhile and Andrew ack'ed
this submission.