core: mediocre workaround for mingw32 who ignores our FP_USE macro.

src/core.h

@@ -33,6 +33,8 @@
 #      define FP_USE(x) __asm__("" : "+f" (x))
 #   elif defined __x86_64__
 #      define FP_USE(x) __asm__("" : "+x" (x))
+#   elif defined _WIN32 /* FIXME: this isn't good */
+#      define FP_USE(x) __asm__("" : "+m" (x))
 #   elif defined __i386__
 #      define FP_USE(x) __asm__("" : "+t" (x))
 #   endif