sigaction: Fix !HAS_REALTIME compilation

In file included from ./include/signal.h:279:0,
				 from libc/sysdeps/linux/x86_64/sigaction.c:22:
./include/bits/sigaction.h:32:29: error: unknown type name 'siginfo_t'
   void (*sa_sigaction)(int, siginfo_t *, void *);

Signed-off-by: Bernhard Reutner-Fischer <rep.dot.nop@gmail.com>

include/signal.h

@@ -98,7 +98,9 @@ typedef __uid_t uid_t;
 /* We need `struct timespec' later on.  */
 # define __need_timespec
 # include <time.h>
+#endif
 
+#if defined __USE_POSIX199309 || defined __USE_XOPEN_EXTENDED
 /* Get the `siginfo_t' type plus the needed symbols.  */
 # include <bits/siginfo.h>
 #endif