Fix build.

Change-Id: I71cde79263d5f5a8382865b8151f65c5c05ea17b
diff --git a/libc/include/sys/socket.h b/libc/include/sys/socket.h
index b6107a5..db6902a 100644
--- a/libc/include/sys/socket.h
+++ b/libc/include/sys/socket.h
@@ -45,6 +45,8 @@
 #define sockaddr_storage __kernel_sockaddr_storage
 typedef unsigned short sa_family_t;
 
+struct timespec;
+
 #ifdef __mips__
 #define SOCK_DGRAM      1
 #define SOCK_STREAM     2