Change -mno-mmx to be more compatible with gcc. Specifically, -mno-mmx should not imply -mno-sse.
Note that because we don't usually touch the MMX registers anyway, all -mno-mmx needs to do is tweak the x86-32 calling convention a little for vectors that look like MMX vectors, and prevent the definition of __MMX__.
clang doesn't actually stop the user from using MMX inline asm operands or MMX builtins in -mno-mmx mode; as a QOI issue, it would be nice to diagnose, but I doubt it really matters much.
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git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@134770
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