mingw32: fix MSC-style underscore consistency

src/racket/sconfig.h

@@ -608,7 +608,14 @@
 /* MS Visual C++ likes underscore prefixes */
 #if defined(_MSC_VER)
 # define MSC_IZE(x) _ ## x
+# define M_MSC_IZE(x) MSC_IZE(x)
 # define DIRECT_INCLUDE
+# else
+# define M_MSC_IZE(x) x
+#endif
+
+#if defined(__MINGW32__)
+# define MSC_IZE(x) _ ## x
 #endif
 
 #ifdef __BORLANDC__

src/racket/src/schpriv.h

@@ -199,7 +199,7 @@ void scheme_clear_ephemerons(void);
 #define BITS_PER_MZSHORT (8 * sizeof(mzshort))
 
 #ifndef NO_INLINE_KEYWORD
-# define MZ_INLINE MSC_IZE(inline)
+# define MZ_INLINE M_MSC_IZE(inline)
 #else
 # define MZ_INLINE /* empty */
 #endif