socketcall: re-add guard

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

libc/sysdeps/linux/common/__socketcall.c

@@ -8,7 +8,18 @@
  */
 
 #include <sys/syscall.h>
+
+/* At the time of this writing,
+ * several arches provide the individual calls and do _not_ go through
+ * this demuxer.
+ *
+ * Verify all arches supported by your kernel before you remove the
+ * guard below!
+ */
+#ifdef __NR_socketcall
 #include <sys/socket.h>
 
 #define __NR___socketcall __NR_socketcall
 _syscall2(int, __socketcall, int, call, unsigned long *, args)
+
+#endif