SDL_config_os2.h: undefine HAVE_TRUNC trunc() exists only in OpenWatcom 2.0 fork, and its implementation already is the same as the fallback we have here..
diff --git a/include/SDL_config_os2.h b/include/SDL_config_os2.h
index 16a690b..63d2880 100644
--- a/include/SDL_config_os2.h
+++ b/include/SDL_config_os2.h
@@ -180,7 +180,7 @@
/* #undef HAVE_SQRTF */
#define HAVE_TAN 1
/* #undef HAVE_TANF */
-#define HAVE_TRUNC 1
+/* #undef HAVE_TRUNC */
/* #undef HAVE_TRUNCF */
#endif /* SDL_config_os2_h_ */