mysqlcppconn: make mysqlcppconn_configure depend on one .o file

so that the build directory at least exists

Change-Id: Iaddeb59d60e81b0823ded73c85c2ffd19244d3c2

external/mysqlcppconn/Library_mysqlcppconn.mk

@@ -76,7 +76,7 @@ $(eval $(call gb_Library_add_generated_exception_objects,mysqlcppconn,\
 
 $(WORKDIR)/GenCxxObject/UnpackedTarball/mysqlcppconn/driver/mysql_metadata.o $(WORKDIR)/GenCxxObject/UnpackedTarball/mysqlcppconn/driver/mysql_driver.o: mysqlcppconn_configure
 
-mysqlcppconn_configure: $(call gb_UnpackedTarball_get_target,mysqlcppconn)
+mysqlcppconn_configure: $(call gb_UnpackedTarball_get_target,mysqlcppconn) $(WORKDIR)/GenCxxObject/UnpackedTarball/mysqlcppconn/driver/mysql_util.o
 	cd $(WORKDIR)/GenCxxObject/UnpackedTarball/mysqlcppconn && cmake ../../../UnpackedTarball/mysqlcppconn/
 
 .PHONY: mysqlcppconn_configure