re-enabled YJIT on x64-mswin64

note that YJIT does not work correctly on the platform now.

yjit.h

@@ -16,7 +16,7 @@
 #endif
 
 // We generate x86 assembly
-#if defined(__x86_64__)
+#if (defined(__x86_64__) && !defined(_WIN32)) || (defined(_WIN32) && defined(_M_AMD64)) // x64 platforms without mingw/msys
 # define YJIT_SUPPORTED_P 1
 #else
 # define YJIT_SUPPORTED_P 0