Fix errno conflict

Newlib defines errno as

	#define errno (*__errno())

In case this is expanded in a function parameter, e.g.

	void f(int errno) { ... }

then we have a function pointer parameter instead of the integer scalar.

freebsd/sys/netinet/udp_usrreq.c

@@ -33,6 +33,10 @@
  *	@(#)udp_usrreq.c	8.6 (Berkeley) 5/23/95
  */
 
+#ifdef __rtems__
+#include <errno.h>
+#undef errno
+#endif /* __rtems__ */
 #include <sys/cdefs.h>
 __FBSDID("$FreeBSD$");