include: Add the msvcrt/crtdefs.h header and include it where needed.
diff --git a/include/msvcrt/math.h b/include/msvcrt/math.h
index 4192378..5aaf7ab 100644
--- a/include/msvcrt/math.h
+++ b/include/msvcrt/math.h
@@ -8,9 +8,8 @@
 
 #ifndef __WINE_MATH_H
 #define __WINE_MATH_H
-#ifndef __WINE_USE_MSVCRT
-#define __WINE_USE_MSVCRT
-#endif
+
+#include <crtdefs.h>
 
 #include <pshpack8.h>