[Interest] Figuring out qmake and -static install use

[Tuncer Ayaz]

I'm trying to fix static linking against Qt5 in mkvtoolnix-gui, and
because it has its own autoconf+make build system, I need to figure
out how to link in the archives (.a) such that there's no runtime
error trying to load a non-existent xcb plugin .so for a Qt5.5 install
that was built with "./configure -static [...]". I know that the Qt5.5
install works flawlessly when linking qcachegrind, so it should be
enough to understand what qmake does and replicate that in
mkvtoolnix's build system. Any pointers for me to investigate?