_mingw_mac.h: bump to 15.x

Signed-off-by: Jonathan Yong <10walls@gmail.com>

mingw-w64-headers/crt/_mingw_mac.h

diff --git a/mingw-w64-headers/crt/_mingw_mac.h b/mingw-w64-headers/crt/_mingw_mac.h
index 1add16b..dae10e7 100644
--- a/mingw-w64-headers/crt/_mingw_mac.h
+++ b/mingw-w64-headers/crt/_mingw_mac.h
@@ -14,7 +14,7 @@
 #define __MINGW64_STRINGIFY(x) \
   __STRINGIFY(x)
 
-#define __MINGW64_VERSION_MAJOR 14
+#define __MINGW64_VERSION_MAJOR 15
 #define __MINGW64_VERSION_MINOR 0
 #define __MINGW64_VERSION_BUGFIX 0