make the feature file search do fewer useless stat()s
make the feature file search do fewer useless stat()s

qmake ensures that the file name ends with .prf, so there is no point if
we try it without first.

enricoros/k-qt-creator-inspector,richardmg/qtcreator,Distrotech/qtcreator,sandsmark/qtcreator-minimap,enricoros/k-qt-creator-inspector,KDE/android-qt-creator,sandsmark/qtcreator-minimap,maui-packages/qt-creator,malikcjm/qtcreator,Distrotech/qtcreator,yinyunqiao/qtcreator,omniacreator/qtcreator,farseerri/git_code,amyvmiwei/qt-creator,darksylinc/qt-creator,renatofilho/QtCreator,martyone/sailfish-qtcreator,colede/qtcreator,xianian/qt-creator,Distrotech/qtcreator,farseerri/git_code,pcacjr/qt-creator,maui-packages/qt-creator,amyvmiwei/qt-creator,omniacreator/qtcreator,jonnor/qt-creator,azat/qtcreator,colede/qtcreator,darksylinc/qt-creator,KDE/android-qt-creator,ostash/qt-creator-i18n-uk,richardmg/qtcreator,dmik/qt-creator-os2,kuba1/qtcreator,Distrotech/qtcreator,richardmg/qtcreator,yinyunqiao/qtcreator,malikcjm/qtcreator,azat/qtcreator,dmik/qt-creator-os2,xianian/qt-creator,martyone/sailfish-qtcreator,hdweiss/qt-creator-visualizer,KDE/android-qt-creator,ostash/qt-creator-i18n-uk,farseerri/git_code,jonnor/qt-creator,hdweiss/qt-creator-visualizer,yinyunqiao/qtcreator,bakaiadam/collaborative_qt_creator,omniacreator/qtcreator,enricoros/k-qt-creator-inspector,KDAB/KDAB-Creator,KDE/android-qt-creator,farseerri/git_code,azat/qtcreator,danimo/qt-creator,ostash/qt-creator-i18n-uk,martyone/sailfish-qtcreator,sandsmark/qtcreator-minimap,amyvmiwei/qt-creator,enricoros/k-qt-creator-inspector,enricoros/k-qt-creator-inspector,duythanhphan/qt-creator,bakaiadam/collaborative_qt_creator,xianian/qt-creator,omniacreator/qtcreator,AltarBeastiful/qt-creator,Distrotech/qtcreator,Distrotech/qtcreator,danimo/qt-creator,sandsmark/qtcreator-minimap,pcacjr/qt-creator,azat/qtcreator,ostash/qt-creator-i18n-uk,darksylinc/qt-creator,pcacjr/qt-creator,AltarBeastiful/qt-creator,duythanhphan/qt-creator,AltarBeastiful/qt-creator,farseerri/git_code,danimo/qt-creator,malikcjm/qtcreator,renatofilho/QtCreator,kuba1/qtcreator,kuba1/qtcreator,AltarBeastiful/qt-creator,martyone/sailfish-qtcreator,KDAB/KDAB-Creator,martyone/sailfish-qtcreator,bakaiadam/collaborative_qt_creator,jonnor/qt-creator,xianian/qt-creator,kuba1/qtcreator,duythanhphan/qt-creator,duythanhphan/qt-creator,bakaiadam/collaborative_qt_creator,omniacreator/qtcreator,duythanhphan/qt-creator,AltarBeastiful/qt-creator,renatofilho/QtCreator,KDAB/KDAB-Creator,omniacreator/qtcreator,malikcjm/qtcreator,xianian/qt-creator,enricoros/k-qt-creator-inspector,dmik/qt-creator-os2,jonnor/qt-creator,yinyunqiao/qtcreator,syntheticpp/qt-creator,omniacreator/qtcreator,xianian/qt-creator,jonnor/qt-creator,danimo/qt-creator,ostash/qt-creator-i18n-uk,maui-packages/qt-creator,pcacjr/qt-creator,bakaiadam/collaborative_qt_creator,colede/qtcreator,danimo/qt-creator,martyone/sailfish-qtcreator,xianian/qt-creator,syntheticpp/qt-creator,ostash/qt-creator-i18n-uk,pcacjr/qt-creator,KDE/android-qt-creator,syntheticpp/qt-creator,duythanhphan/qt-creator,Distrotech/qtcreator,amyvmiwei/qt-creator,yinyunqiao/qtcreator,richardmg/qtcreator,KDAB/KDAB-Creator,kuba1/qtcreator,bakaiadam/collaborative_qt_creator,duythanhphan/qt-creator,darksylinc/qt-creator,KDAB/KDAB-Creator,KDAB/KDAB-Creator,kuba1/qtcreator,dmik/qt-creator-os2,malikcjm/qtcreator,jonnor/qt-creator,danimo/qt-creator,martyone/sailfish-qtcreator,maui-packages/qt-creator,kuba1/qtcreator,ostash/qt-creator-i18n-uk,danimo/qt-creator,renatofilho/QtCreator,syntheticpp/qt-creator,AltarBeastiful/qt-creator,syntheticpp/qt-creator,colede/qtcreator,darksylinc/qt-creator,darksylinc/qt-creator,colede/qtcreator,xianian/qt-creator,KDE/android-qt-creator,amyvmiwei/qt-creator,farseerri/git_code,azat/qtcreator,maui-packages/qt-creator,AltarBeastiful/qt-creator,amyvmiwei/qt-creator,dmik/qt-creator-os2,richardmg/qtcreator,colede/qtcreator,amyvmiwei/qt-creator,sandsmark/qtcreator-minimap,darksylinc/qt-creator,bakaiadam/collaborative_qt_creator,malikcjm/qtcreator,kuba1/qtcreator,yinyunqiao/qtcreator,syntheticpp/qt-creator,KDE/android-qt-creator,maui-packages/qt-creator,dmik/qt-creator-os2,danimo/qt-creator,pcacjr/qt-creator,renatofilho/QtCreator,KDE/android-qt-creator,azat/qtcreator,farseerri/git_code,martyone/sailfish-qtcreator,malikcjm/qtcreator,enricoros/k-qt-creator-inspector,renatofilho/QtCreator,danimo/qt-creator,martyone/sailfish-qtcreator,xianian/qt-creator,kuba1/qtcreator,darksylinc/qt-creator,colede/qtcreator,richardmg/qtcreator,farseerri/git_code,yinyunqiao/qtcreator,amyvmiwei/qt-creator,hdweiss/qt-creator-visualizer,hdweiss/qt-creator-visualizer,richardmg/qtcreator,maui-packages/qt-creator,hdweiss/qt-creator-visualizer,syntheticpp/qt-creator,hdweiss/qt-creator-visualizer,sandsmark/qtcreator-minimap,pcacjr/qt-creator,dmik/qt-creator-os2,AltarBeastiful/qt-creator