[X86] Prevent assertion when calling a function that returns double with -mno-sse2 on x86-64.
[X86] Prevent assertion when calling a function that returns double with -mno-sse2 on x86-64.

As seen in the most recent updates to PR10498

git-svn-id: ffe668792ed300d6c2daa1f6eba2e0aa28d7ec6c@372197 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang