[X86] Enable fp128 as a legal type with SSE1 rather than with MMX.
FP128 values are passed in xmm registers so should be asssociated
with an SSE feature rather than MMX which uses a different set
llc enables sse1 and sse2 by default with x86_64. But does not
enable mmx. Clang enables all 3 features by default.
I've tried to add command lines to test with -sse
where possible, but any test that returns a value in an xmm
register fails with a fatal error with -sse since we have no
defined ABI for that scenario.