include/sys/mman.h says that msync exists only on MMU.

Make msync.c agree on this.

libc/sysdeps/linux/common/msync.c

@@ -14,9 +14,13 @@
 
 #include <sys/mman.h>
 
+#ifdef __ARCH_USE_MMU__
+
 extern __typeof(msync) __libc_msync;
 #define __NR___libc_msync __NR_msync
 _syscall3(int, __libc_msync, void *, addr, size_t, length, int, flags);
 weak_alias(__libc_msync,msync)
 
 #endif
+
+#endif