Before this, the paths in pkg-config (.pc) and libtool (.la) files of
submodules are all pointing to qtbase.
* gnu/packages/qt.scm (qtbase)[native-inputs]: Move 'which' to
'propagated-inputs'.
[arguments]: Rename 'patch-qt_config.prf' phase to 'patch-mkspecs' and
patch more qmake spec files there.
(qtsvg)[arguments]: Add 'configure-qmake' phase.