gdb: add source targets for gdbserver/gdbhost

So it gets handled by make source / external-deps

Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>

toolchain/gdb/gdb.mk

@@ -162,6 +162,8 @@ endif
 
 gdbserver: $(TARGET_DIR)/usr/bin/gdbserver
 
+gdbserver-source: $(DL_DIR)/$(GDB_SOURCE)
+
 gdbserver-clean:
 	-$(MAKE) -C $(GDB_SERVER_DIR) clean
 
@@ -209,6 +211,8 @@ $(TARGET_CROSS)gdb: $(GDB_HOST_DIR)/gdb/gdb
 
 gdbhost: $(TARGET_CROSS)gdb
 
+gdbhost-source: $(DL_DIR)/$(GDB_SOURCE)
+
 gdbhost-clean:
 	-$(MAKE) -C $(GDB_HOST_DIR) clean