enable fcntl nocancel prototype for all threads

The cancel logic always uses this function even when !NPTL, so always
enable the prototype to avoid warnings.

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

include/fcntl.h

@@ -234,9 +234,7 @@ extern int posix_fallocate64 (int __fd, __off64_t __offset, __off64_t __len);
 # endif
 #endif
 
-#ifdef __UCLIBC_HAS_THREADS_NATIVE__
 extern int __fcntl_nocancel (int fd, int cmd, ...);
-#endif
 
 __END_DECLS