qt4: fix static building if libglib-2.0 is enabled

Here we're seeing another issue with static builds.
Problem is Qt's configuration system post-processes output of pkg-config
removing duplicate entries. That's fine for dynamic builds - all symbols
will be resolved in runtime but for static builds we need to specify
explicit and correct list of libs.

See more explanations in the patch itself.

This patch was sent in Qt's Gerrit for review and could be seen here:
https://codereview.qt-project.org/#/c/145967/

Fixes a couple of qt4 build failures:
http://autobuild.buildroot.net/results/174/174c6e47eb761f9897275b6fedff742ace2f3081
http://autobuild.buildroot.net/results/273/273676f1deee986a205b63e92cd6042c29ba1578
http://autobuild.buildroot.net/results/4f9/4f92d1316e786d8bb3c16b748f1ab731562540e3


and many others.

Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>
Cc: Lada Trimasova <ltrimas@synopsys.com>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>