You could add any of these (-mmmx -msse -msse2 -msse3 -m3dnow) to the CFLAGS if {cat /proc/cpuinfo | grep flags } has mmx, sse, sse2, sse3, 3dnow, respectively. However one should note that if there is multiple sse flags that only the latest should be used. Furthermore -mfpmath=sse (or -mfpmath=sse,387 in future versions of gcc) should be set if the flags have any sse.
no, you should not set -mfpmath=sse
*** Bug 170788 has been marked as a duplicate of this bug. ***
No. your -march options will apply the correct -m{mmx*,sse*,3dnow*} options automatically.
