Restore compatibility with Qt 4

The test system is Slackware 14.2, which uses Qt 4.8.7.

* WANT_WIN_QT4 is defined, and has the expected meaning. Qt 5 is still
  the default.

* The QT_NO_SOUND macro now excludes all headers and declarations
  relating to sound; the multimedia package is not needed to build
  (on any Qt 4, 5 or 6).

* A new function, nh_qsprintf, replaces QString::asprintf, for Qt
  older than 5.5. These versions do not have QString::asprintf.

* DYNAMIC_STATUSLINES is disabled for Qt older than 5.9. These versions
  do not have QSplitter::replaceWidget.

win/Qt/qt_main.cpp

@@ -13,7 +13,7 @@ extern "C" {
 #include <QtGui/QtGui>
 #if QT_VERSION >= 0x060000
 #include <QtGui/QShortcut>
-#else
+#elif QT_VERSION >= 0x050000
 #include <QtWidgets/QShortcut>
 #endif
 
@@ -463,7 +463,7 @@ aboutMsg()
         *p = '\0';
     /* it's also long; break it into two pieces */
     (void) strsubst(vbuf, " - ", "\n- ");
-    QString msg = QString::asprintf(
+    QString msg = nh_qsprintf(
         // format
         "NetHack-Qt is a version of NetHack built using" // no newline
 #ifdef KDE
@@ -1034,7 +1034,7 @@ void NetHackQtMainWindow::doQuit(bool)
     // nethack's #quit command itself) but this routine is unconditional
     // in case someone wants to change that
 #ifdef MACOS
-    QString info = QString::asprintf("This will end your NetHack session.%s",
+    QString info = nh_qsprintf("This will end your NetHack session.%s",
                  !g.program_state.something_worth_saving ? ""
                  : "\n(Cancel quitting and use the Save command"
                    "\nto save your current game.)");