[Headers] [ARM64EC] Fix extra tokens inside intrin0.h preprocessor directive (#112066)

Fixes https://github.com/llvm/llvm-project/pull/87717.

(cherry picked from commit 9bf68c2400e8966511332dfbf5c0f05e8a3300fa)

clang/lib/Headers/intrin0.h

@@ -44,7 +44,7 @@ unsigned char _InterlockedCompareExchange128_rel(__int64 volatile *_Destination,
                                                  __int64 *_ComparandResult);
 #endif
 
-#ifdef __x86_64__ && !defined(__arm64ec__)
+#if defined(__x86_64__) && !defined(__arm64ec__)
 unsigned __int64 _umul128(unsigned __int64, unsigned __int64,
                           unsigned __int64 *);
 unsigned __int64 __shiftleft128(unsigned __int64 _LowPart,

clang/test/Headers/ms-intrin.cpp

 // RUN: %clang_cc1 -triple i386-pc-win32 -target-cpu pentium4 \
 // RUN:     -fms-extensions -fms-compatibility -fms-compatibility-version=17.00 \
-// RUN:     -ffreestanding -fsyntax-only -Werror \
+// RUN:     -ffreestanding -fsyntax-only -Werror -Wsystem-headers \
 // RUN:     -isystem %S/Inputs/include %s
 
 // RUN: %clang_cc1 -triple i386-pc-win32 -target-cpu broadwell \
 // RUN:     -fms-extensions -fms-compatibility -fms-compatibility-version=17.00 \
-// RUN:     -ffreestanding -emit-obj -o /dev/null -Werror \
+// RUN:     -ffreestanding -emit-obj -o /dev/null -Werror -Wsystem-headers \
 // RUN:     -isystem %S/Inputs/include %s
 
 // RUN: %clang_cc1 -triple x86_64-pc-win32  \
 // RUN:     -fms-extensions -fms-compatibility -fms-compatibility-version=17.00 \
-// RUN:     -ffreestanding -emit-obj -o /dev/null -Werror \
+// RUN:     -ffreestanding -emit-obj -o /dev/null -Werror -Wsystem-headers \
 // RUN:     -isystem %S/Inputs/include %s
 
 // RUN: %clang_cc1 -triple thumbv7--windows \
 // RUN:     -fms-compatibility -fms-compatibility-version=17.00 \
-// RUN:     -ffreestanding -fsyntax-only -Werror \
+// RUN:     -ffreestanding -fsyntax-only -Werror -Wsystem-headers \
 // RUN:     -isystem %S/Inputs/include %s
 
 // RUN: %clang_cc1 -triple aarch64--windows \
 // RUN:     -fms-compatibility -fms-compatibility-version=17.00 \
-// RUN:     -ffreestanding -fsyntax-only -Werror \
+// RUN:     -ffreestanding -fsyntax-only -Werror -Wsystem-headers \
 // RUN:     -isystem %S/Inputs/include %s
 
 // RUN: %clang_cc1 -triple arm64ec--windows \
 // RUN:     -fms-compatibility -fms-compatibility-version=17.00 \
-// RUN:     -ffreestanding -fsyntax-only -Werror \
+// RUN:     -ffreestanding -fsyntax-only -Werror -Wsystem-headers \
 // RUN:     -isystem %S/Inputs/include %s
 
 // REQUIRES: x86-registered-target