LibC: Add flag SO_BROADCAST so we can at least build programs that use it

Author: https://github.com/xspager 🔰
Commit: 57c9f77921
Pull-request: https://github.com/SerenityOS/serenity/pull/4290

Libraries/LibC/sys/socket.h

@@ -107,6 +107,7 @@ enum {
     SO_BINDTODEVICE,
     SO_KEEPALIVE,
     SO_TIMESTAMP,
+    SO_BROADCAST,
 };
 #define SO_RCVTIMEO SO_RCVTIMEO
 #define SO_SNDTIMEO SO_SNDTIMEO
@@ -117,6 +118,7 @@ enum {
 #define SO_BINDTODEVICE SO_BINDTODEVICE
 #define SO_KEEPALIVE SO_KEEPALIVE
 #define SO_TIMESTAMP SO_TIMESTAMP
+#define SO_BROADCAST SO_BROADCAST
 
 enum {
     SCM_TIMESTAMP,