build: fix xconfig target

build: fix xconfig target

`make xconfig` fails with following linking error of qconf binary:

 g++ -lQt5Widgets -lQt5Gui -lQt5Core -o qconf qconf.o zconf.tab.o
 /usr/bin/ld: qconf.o: in function ConfigList::metaObject() const': qconf.cc:(.text+0x3eb): undefined reference to QObjectData::dynamicMetaObject() const'
 /usr/bin/ld: qconf.o: in function `ConfigList::qt_metacast(char const*)': link error.

which is caused by the wrong order of the linked objects/libraries so
this patch reorders the linker's arguments which makes the qconf compile
again.

Signed-off-by: leo chung <gewalalb@gmail.com>
[commit subject and message tweaks, whitespace fix]
Signed-off-by: Petr Štetiar <ynezz@true.cz>