--- Libc/Libc-498/include/alloca.h
+++ Libc/Libc-1669.40.2/include/alloca.h
@@ -26,15 +26,13 @@
 
 #include <sys/cdefs.h>
 #include <_types.h>
+#include <sys/_types/_size_t.h>
 
-#ifndef	_SIZE_T
-#define	_SIZE_T
-typedef	__darwin_size_t	size_t;
-#endif
-
+#ifndef UNIFDEF_DRIVERKIT
 __BEGIN_DECLS
 void	*alloca(size_t);		/* built-in for gcc */
 __END_DECLS
+#endif /* UNIFDEF_DRIVERKIT */
 
 #if defined(__GNUC__) && __GNUC__ >= 3
 /* built-in for gcc 3 */