[X86][InlineAsm][Ms Compatibility]Prefer variable name over a register when the two collides

On MS-style, the following snippet:

int eax;
__asm mov eax, ebx

should yield loading of ebx, into the location pointed by the variable eax

This patch sees to it.

Currently, a reg-to-reg move would have been invoked.

clang: D34740

Differential Revision: https://reviews.llvm.org/D34739

llvm-svn: 308866