MFC several improvements in lib32 build:

1.528: Default to producing 'k8' COMPAT_32BIT bits, but allow override.
1.529: SSE2 comes thru the users choice of CPUTYPE.
1.531: Use cross-compile friendly spelling of CPUTYPE.
1.567: Clean the lib32 object directory with cleandir rather than rm -rf.
1.568: Resurrect one of the patches from attic and refine the

lib32 build somewhat.  Specifically, instead of spamming
${CC} et al with -I${LIB32TMP}/usr/include which can be
harmful (as has been demonstrated by the ncursesw WIP),
use slightly different approach to achieve the same goal.
This also simplifies things a bit.

Approved by: delphij (mentor)