Bug#888963: $$QMAKE_QMAKE -query does not work for cross compilation

[Helmut Grohne <helmut@subdivi.de>]

Package: qt5-qmake
Version: 5.9.2+dfsg-7
User: helmutg@debian.org
Usertags: rebootstrap
Control: affects -1 + src:pokerth

pokerth uses "system(qmake -query QT_INSTALL_LIBS). It shouldn't use
bare qmake but use $$QMAKE_QMAKE instead for recursive invocations.
Still doing so fails, because qmake -query only works correctly when
-query is the first argument (as we noticed for the qmake cross
wrapper). Thus even $$QMAKE_QMAKE -query QT_INSTALL_LIBS does not work
as expected.

Thus I believe that we need to ensure that $$QMAKE_QMAKE points to
something that works with -query. Incidentally, we have that already:
/usr/bin/${DEB_HOST_GNU_TYPE}-qmake. So if you agree here, should we
simply update dh_auto_configure to use the wrapper rather than passing
all the same flags as the wrapper does?

If yes, we should come up with a patch and reassign to debhelper. If no,
how should we handle this case?

Helmut