buildgcc: Do not download GDB source code if run with --skip-gdb

Change-Id: Ida3680418fdd3136752d51cc19f3e14111c12131
Signed-off-by: Peter Stuge <peter@stuge.se>
Reviewed-on: http://review.coreboot.org/175
Tested-by: build bot (Jenkins)

util/crossgcc/buildgcc

@@ -189,6 +189,7 @@ done
 GDB_PACKAGE="GDB"
 if [ $SKIPGDB -eq 1 ]; then
 	printf "Will skip GDB ... ${green}ok${NC}\n"
+	GDB_ARCHIVE=""
 	GDB_PACKAGE=""
 fi