[X86] Correctly use SSE registers if no-x87 is selected.

Fix use of SSE1 registers for f32 ops in no-x87 mode.

Notably, allow use of SSE instructions for f32 operations in 64-bit
mode (but not 32-bit which is disallowed by callign convention).

Also avoid translating memset/memcopy/memmove into SSE registers
without X87 for 32-bit mode.

This fixes PR38738.

Reviewers: nickdesaulniers, craig.topper

Subscribers: hiraditya, llvm-commits

Differential Revision: https://reviews.llvm.org/D52555

llvm-svn: 343689