QT_LIBDIR gets added before MODULE_LIBS

Commits 0fc4f2b4 ("qtAddModule(): put search paths directly into LIBS{,_PRIVATE}") and e38af234 ("dispose of QMAKE_LIBDIR_FLAGS, "demote" QMAKE_FRAMEWORKPATH_FLAGS") have caused a regression compared to Qt4 when an mkspec sets QMAKE_LIBDIR to a directory where Qt's libraries are installed. unsupported/freebsd-clang/qmake.conf, for example, sets QMAKE_LIBDIR to /usr/local/lib.

If one has an older version of Qt5 installed in /usr/local/lib and builds a more recent one, this may happen:

clang++ -Wl,--no-undefined -Wl,-O1 -pthread -Wl,-rpath,/usr/local/lib -shared -o libqjpeg.so .obj/qjpeghandler.o  .obj/main.o  .obj/moc_main.o  -L/usr/local/lib -ljpeg -L/path/to/my/build/dir/lib -lQt5Gui -lQt5Core -lGL
.obj/qjpeghandler.o: In function `write_jpeg_image(QImage const&, QIODevice*, int, QString const&)':
../../../gui/image/qjpeghandler.cpp:(.text+0x24f6): undefined reference to `QImage::convertToFormat_inplace(QImage::Format, QFlags<Qt::ImageConversionFlag>)'
../../../gui/image/qjpeghandler.cpp:(.text+0x253e): undefined reference to `QImage::convertToFormat_helper(QImage::Format, QFlags<Qt::ImageConversionFlag>) const'

/path/to/my/build/dir/lib/libQt5Gui.so should be preferred over /usr/local/lib/libQt5Gui.so.

The solution I could think of so far involves prepending MODULE_LIBS instead of appending it in qt_functions.prf's qtAddModule and appending QMAKE_LIBDIR/QMAKE_LIBDIR_FLAGS to QMAKE_LIBS instead of prepending in qmake's Makefile generator, but I'm obviously not sure if this is stupid and will break half of qmake's use cases Should I send a patch nonetheless?