MMX argument passing fixes:

MMX argument passing fixes:
On Darwin / Linux x86-32, v8i8, v4i16, v2i32 values are passed in MM[0-2].
On Darwin / Linux x86-32, v1i64 values are passed in memory.
On Darwin x86-64, v8i8, v4i16, v2i32 values are passed in XMM[0-7].
On Darwin x86-64, v1i64 values are passed in 64-bit GPRs.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@50257 91177308-0d34-0410-b5e6-96231b3b80d8