fix-missing-win32-constant-ruby200.diff

--- include/ruby/win32.h.orig	2015-07-16 17:52:17.882015422 +0900
+++ include/ruby/win32.h	2015-07-16 17:52:52.138016369 +0900
@@ -790,6 +790,13 @@ rb_w32_pow(double x, double y)
     return powl(x, y);
 }
 #elif defined(__MINGW64_VERSION_MAJOR)
+#ifndef _PC_64
+#define _PC_64 0x00000000
+#endif
+
+#ifndef _MCW_PC
+#define _MCW_PC 0x00030000
+#endif
 /*
  * Set floating point precision for pow() of mingw-w64 x86.
  * With default precision the result is not proper on WinXP.