[COFF, ARM64] Add __nop intrinsic

[efriedma]

LGTM

I'm assuming this isn't on the list of intrinsics that we must not implement as an inline function in intrin.h... if it is, we'll have to reimplement it at some point. But this is clearly an improvement, in any case.

[rnk]

lgtm

cfe/trunk/lib/Headers/intrin.h

_xgetbv(unsigned int __xcr_no) {
   unsigned int __eax, __edx;
   __asm__ ("xgetbv" : "=a" (__eax), "=d" (__edx) : "c" (__xcr_no));
   return ((unsigned __int64)__edx << 32) | __eax;
 }
 static __inline__ void __DEFAULT_FN_ATTRS
 __halt(void) {
   __asm__ volatile ("hlt");
 }
+#endif
+
+#if defined(__i386__) || defined(__x86_64__) || defined(__aarch64__)
 static __inline__ void __DEFAULT_FN_ATTRS
 __nop(void) {
   __asm__ volatile ("nop");
 }
 #endif
 
 /*----------------------------------------------------------------------------*\
 |* MS AArch64 specific

cfe/trunk/test/Headers/ms-arm64-intrin.cpp

+// RUN: %clang_cc1 -triple arm64-windows \
+// RUN: -fms-compatibility -fms-compatibility-version=17.00 \
+// RUN: -ffreestanding -fsyntax-only -Werror \
+// RUN: -isystem %S/Inputs/include %s -S -o - 2>&1 | FileCheck %s
+
+// REQUIRES: aarch64-registered-target
+
+#include <intrin.h>
+
+void f() {
+// CHECK: nop
+  __nop();
+}