[TESTING] ssse3 backport from gcc 4.3

I have prepared a patch that finishes the "core2" support part and
backports from gcc-4.3
the SSSE3 instruction set (-mssse3, -mno-ssse3).
It is enabled for -march=core2 by default.

Testing and comments are welcome.

Patch:
http://people.freebsd.org/~mm/patches/head-gcc-ssse3.patch

The backport covers three GPLv2 revisions from gcc 4.3:
http://gcc.gnu.org/viewcvs?view=revision&revision=117958 (applies cleanly)
http://gcc.gnu.org/viewcvs?view=revision&revision=121687 (small adjustment)
http://gcc.gnu.org/viewcvs?view=revision&revision=121726 (small adjustment)
http://gcc.gnu.org/viewcvs?view=revision&revision=123639 (small adjustment)