[X86][inline-asm] Add support for MS 'EVEN' directive

[coby]

Summary

MS assembly syntax provide us with the 'EVEN' directive as a synonymous to at&t '.even'.
This patch include the (small, simple) changes need to allow it.

llvm-side:
https://reviews.llvm.org/D27417

Differential Revision: https://reviews.llvm.org/D27418

[m_zuckerman]

lgtm

cfe/trunk/test/CodeGen/ms-inline-asm-EVEN.c

+// RUN: %clang_cc1 %s -triple i386-unknown-unknown -fasm-blocks -emit-llvm -o - | FileCheck %s
+
+// CHECK: .byte 64
+// CHECK: .byte 64
+// CHECK: .byte 64
+// CHECK:  .even
+void t1() {
+  __asm {
+    .byte 64
+    .byte 64
+    .byte 64
+    EVEN
+    mov eax, ebx
+  }
+}