make the value of QMAKE_QMAKE somewhat less magic
make the value of QMAKE_QMAKE somewhat less magic

the generators change the value of QMAKE_QMAKE, so it is unwise to
"redirect" it to a hidden builtin which is reset each time.

in particular, this fixes qmake generating makefiles without an absolute
path to qmake itself - the initial quoting of the filename will make the
variable "real", so contains() will start working for it.
(cherry picked from commit 31e1fb9103e6d6657c1153f5c30e149087568042)

igor-sfdc/qt-wk,igor-sfdc/qt-wk,igor-sfdc/qt-wk,igor-sfdc/qt-wk,igor-sfdc/qt-wk,pruiz/wkhtmltopdf-qt,igor-sfdc/qt-wk,pruiz/wkhtmltopdf-qt,igor-sfdc/qt-wk,igor-sfdc/qt-wk,pruiz/wkhtmltopdf-qt,pruiz/wkhtmltopdf-qt,pruiz/wkhtmltopdf-qt,pruiz/wkhtmltopdf-qt,igor-sfdc/qt-wk,pruiz/wkhtmltopdf-qt,pruiz/wkhtmltopdf-qt,igor-sfdc/qt-wk,pruiz/wkhtmltopdf-qt,pruiz/wkhtmltopdf-qt,pruiz/wkhtmltopdf-qt,igor-sfdc/qt-wk