Another attempt to fix building using MINGW. Affects #55

Windows/math.h

@@ -1,7 +1,9 @@
 #pragma once
 #include_next <math.h>
+#ifndef __MINGW32__
 /* "Old" (Pre-2015) Windows headers/libc don't have round. */
 static inline double round(double f)
 {
     return f >= 0? (int)(f + 0.5) : (int)(f - 0.5);
 }
+#endif

Windows/stdio.h

@@ -2,6 +2,7 @@
 #include_next <stdio.h>
 #include <stdlib.h>
 
+#ifndef __MINGW32__
 #ifndef __LIBRETRO__
 static inline int vasprintf(char **str, const char *fmt, va_list args)
 {
@@ -16,6 +17,7 @@ static inline int vasprintf(char **str, const char *fmt, va_list args)
     return ret;
 }
 #endif
+#endif
 
 /* This code is public domain -- Will Hartung 4/9/09 */
 static inline size_t getline(char **lineptr, size_t *n, FILE *stream) {