ifdef Q_?S_* cleanup

- clear up some Q_OS_LINUX vs. Q_OS_UNIX
- clear up Q_WS_* vs. Q_OS_* (relatively theoretical exercise)
- use proper #if-#else cascades instead of free-standing #ifs

src/plugins/qt4projectmanager/qtversionmanager.cpp

@@ -937,8 +937,7 @@ static inline QStringList possibleGuiBinaries(const QString &name)
 {
 #ifdef Q_OS_WIN
     return QStringList(name + QLatin1String(".exe"));
-#endif
-#ifdef Q_OS_MAC // 'Foo.app/Contents/MacOS/Foo'
+#elif defined(Q_OS_MAC) // 'Foo.app/Contents/MacOS/Foo'
     QString upCaseName = name;
     upCaseName[0] = upCaseName.at(0).toUpper();
     QString macBinary = upCaseName;