implement compileTimeMemoryBarrier in arch.h

This has the same implementation as programOrderMemoryBarrier in
x86.h, but makes it available on all architectures.

src/arch.h

@@ -17,6 +17,20 @@ extern "C" void NO_RETURN
 vmJump(void* address, void* base, void* stack, void* thread,
        uintptr_t returnLow, uintptr_t returnHigh);
 
+namespace vm {
+
+inline void
+compileTimeMemoryBarrier()
+{
+#ifdef _MSC_VER
+  _ReadWriteBarrier();
+#else
+  __asm__ __volatile__("": : :"memory");
+#endif
+}
+
+} // namespace vm
+
 #if (defined ARCH_x86_32) || (defined ARCH_x86_64)
 #  include "x86.h"
 #elif defined ARCH_powerpc

src/windows.cpp

@@ -23,7 +23,7 @@
 #undef max
 #undef min
 
-#include "x86.h"
+#include "arch.h"
 #include "system.h"
 
 #define ACQUIRE(s, x) MutexResource MAKE_NAME(mutexResource_) (s, x)

src/x86.h

@@ -161,11 +161,7 @@ trap()
 inline void
 programOrderMemoryBarrier()
 {
-#ifdef _MSC_VER
-  _ReadWriteBarrier();
-#else
-  __asm__ __volatile__("": : :"memory");
-#endif
+  compileTimeMemoryBarrier();
 }
 
 inline void