Update the qmake documentation regarding when the .qmake.cache is processed.
Update the qmake documentation regarding when the .qmake.cache is
processed.

Reviewed-by: TrustMe
(cherry picked from commit 020ced4994bace0ed7f494bec8905afa959f76ed)

RLovelett/qt,RLovelett/qt,pruiz/wkhtmltopdf-qt,RLovelett/qt,igor-sfdc/qt-wk,KDE/qt,KDE/qt,igor-sfdc/qt-wk,radekp/qt,radekp/qt,KDE/qt,radekp/qt,igor-sfdc/qt-wk,pruiz/wkhtmltopdf-qt,igor-sfdc/qt-wk,pruiz/wkhtmltopdf-qt,KDE/qt,RLovelett/qt,pruiz/wkhtmltopdf-qt,KDE/qt,igor-sfdc/qt-wk,igor-sfdc/qt-wk,radekp/qt,pruiz/wkhtmltopdf-qt,igor-sfdc/qt-wk,igor-sfdc/qt-wk,KDE/qt,KDE/qt,RLovelett/qt,radekp/qt,igor-sfdc/qt-wk,radekp/qt,RLovelett/qt,radekp/qt,RLovelett/qt,pruiz/wkhtmltopdf-qt,RLovelett/qt,pruiz/wkhtmltopdf-qt,radekp/qt,pruiz/wkhtmltopdf-qt,igor-sfdc/qt-wk,igor-sfdc/qt-wk,pruiz/wkhtmltopdf-qt,KDE/qt,RLovelett/qt,pruiz/wkhtmltopdf-qt,RLovelett/qt,radekp/qt,RLovelett/qt,pruiz/wkhtmltopdf-qt,radekp/qt