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

[coby]

Summary

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.

llvm: D34739

test/CodeGen/ms-inline-asm-var-name.c

+// REQUIRES: x86-registered-target
+// RUN: %clang_cc1 %s -triple i386-apple-darwin10 -fasm-blocks -emit-llvm -o - | FileCheck %s
+
+void t() {
+  int eax;
+  int Ecx;
+  __asm mov eax, ebx
+  // CHECK: mov $0, ebx
+  __asm add ecx, Ecx
+  // CHECK: add ecx, $1
+}
+