Handle qmake with or without trailing .exe

Handle qmake with or without trailing .exe on windows. Looks like the
extension got lost recently in the generated Makefiles.

Reviewed-by: dt
(cherry picked from commit 5a97f79e0b)

src/plugins/qt4projectmanager/qtversionmanager.cpp

@@ -750,6 +750,8 @@ QString QtVersionManager::findQMakeBinaryFromMakefile(const QString &directory)
                 QString qmakePath = qmake.filePath();
 #ifdef Q_OS_WIN
                 qmakePath = qmakePath.toLower();
+                if (!qmakePath.endsWith(QLatin1String(".exe")))
+                    qmakePath.append(QLatin1String(".exe"));
 #endif
                 // Is qmake still installed?
                 if (QFile::exists(qmakePath))