Define _M_AMD64 for Windows.
@@ -7,6 +7,7 @@ static char x86_64_mirc[]
"#define __amd64__ 1\n"
"#define __x86_64 1\n"
"#define __x86_64__ 1\n"
+ "#define _M_AMD64 1\n"
"#define _M_X64 1\n"
"\n"
"#define __SIZEOF_DOUBLE__ 8\n"
