Revert "GDB: Only build for "unix:" connections if AF_LOCAL is supported."

This reverts commit 98a17ece01.

gdb/common/netstuff.c

@@ -145,9 +145,7 @@ parse_connection_spec (const char *spec, struct addrinfo *hint)
       { "tcp4:", AF_INET,   SOCK_STREAM },
       { "udp6:", AF_INET6,  SOCK_DGRAM },
       { "tcp6:", AF_INET6,  SOCK_STREAM },
-#if HAVE_AF_LOCAL
       { "unix:", AF_LOCAL,  SOCK_STREAM },
-#endif
     };
 
   for (const host_prefix prefix : prefixes)