[Arm64EC] Fix compilation of arm_acle.h (#91281)

Author: efriedma-quic

clang/lib/Headers/arm_acle.h

@@ -109,7 +109,7 @@ __swp(uint32_t __x, volatile uint32_t *__p) {
 #endif
 
 /* 7.7 NOP */
-#if !defined(_MSC_VER) || !defined(__aarch64__)
+#if !defined(_MSC_VER) || (!defined(__aarch64__) && !defined(__arm64ec__))
 static __inline__ void __attribute__((__always_inline__, __nodebug__)) __nop(void) {
   __builtin_arm_nop();
 }

clang/test/Headers/arm-acle-header.c

@@ -7,6 +7,7 @@
 // RUN: %clang_cc1 -x c++ -triple thumbv7-windows -target-cpu cortex-a15 -fsyntax-only -ffreestanding -fms-extensions -fms-compatibility -fms-compatibility-version=19.11 %s
 // RUN: %clang_cc1 -x c++ -triple aarch64-windows -target-cpu cortex-a53 -fsyntax-only -ffreestanding -fms-extensions -fms-compatibility -fms-compatibility-version=19.11 %s
 // RUN: %clang_cc1 -x c++ -triple arm64-apple-ios -target-cpu apple-a7 -fsyntax-only -ffreestanding -fms-extensions %s
+// RUN: %clang_cc1 -x c++ -triple arm64ec-windows -target-cpu cortex-a53 -fsyntax-only -ffreestanding -fms-extensions -fms-compatibility -fms-compatibility-version=19.11 %s
 // expected-no-diagnostics
 
 #include <arm_acle.h>