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_icon.cpp

@@ -35,6 +35,7 @@ extern "C" {
 #endif
 #include "qt_post.h"
 #include "qt_icon.h"
+#include "qt_str.h"
 
 namespace nethack_qt_ {
 
@@ -106,7 +107,7 @@ void NetHackQtLabelledIcon::setLabel(const QString& t, long v, long cv,
     if (v==NoNum) {
 	buf = "";
     } else {
-	buf = QString::asprintf("%ld", v);
+	buf = nh_qsprintf("%ld", v);
     }
     setLabel(t + buf + tail, cv < prev_value);
     prev_value=cv;