create local prototype for __libc_sigaction

libc/signal/sigaction.c

@@ -16,6 +16,7 @@
    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
    02111-1307 USA.  */
 
+#include <features.h>
 #include <errno.h>
 #include <signal.h>
 #include <string.h>
@@ -29,6 +30,10 @@ libc_hidden_proto(memcpy)
    translate it here.  */
 #include <bits/kernel_sigaction.h>
 
+#ifndef LIBC_SIGACTION
+extern __typeof(sigaction) __libc_sigaction;
+#endif
+
 #if defined __NR_rt_sigaction
 
 /* If ACT is not NULL, change the action for SIG to *ACT.