sys/_types.h: Actually unbreak gcc build

Fixes:		19728f31ae ("sys/_types.h: Unbreak gcc build")
Reviewed by:	emaste
Differential Revision:	https://reviews.freebsd.org/D53986

sys/sys/_types.h

@@ -161,7 +161,10 @@ typedef	int		__cpulevel_t;	/* level parameter for cpuset. */
 typedef int		__cpusetid_t;	/* cpuset identifier. */
 typedef __int64_t	__daddr_t;	/* bwrite(3), FIOBMAP2, etc */
 
-#if !defined(__has_feature) || !__has_feature(capabilities)
+#ifndef __has_feature
+#define __has_feature(x)        0
+#endif
+#if !__has_feature(capabilities)
 /*
  * On non-CHERI systems, define __(u)intcap_t to __(u)intptr_t so that
  * hybrid-C code which needs to be explicitly aware of capabilities can