some ports define ENOTSUP

A port or two (like hppa) does define ENOTSUP, so don't assume that
everyone needs this fallback define.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>

libc/sysdeps/linux/common/bits/errno.h

@@ -25,7 +25,9 @@
 # include <linux/errno.h>
 
 /* Linux has no ENOTSUP error code.  */
-# define ENOTSUP EOPNOTSUPP
+# ifndef ENOTSUP
+#  define ENOTSUP EOPNOTSUPP
+# endif
 
 /* Older Linux versions also had no ECANCELED error code.  */
 # ifndef ECANCELED