Only pass -lQt5PlatformSupport if >=Qt5.6

build-aux/m4/bitcoin_qt.m4

@@ -343,7 +343,9 @@ AC_DEFUN([_BITCOIN_QT_FIND_STATIC_PLUGINS],[
          PKG_CHECK_MODULES([QTPRINT], [Qt5PrintSupport], [QT_LIBS="$QTPRINT_LIBS $QT_LIBS"])
        fi
      else
-       QT_LIBS="-lQt5PlatformSupport $QT_LIBS"
+       if ${PKG_CONFIG} --exists "Qt5Core >= 5.6" 2>/dev/null; then
+         QT_LIBS="-lQt5PlatformSupport $QT_LIBS"
+       fi
      fi
      ])
   else

src/qt/bitcoin.cpp

@@ -533,6 +533,9 @@ int main(int argc, char *argv[])
     // Generate high-dpi pixmaps
     QApplication::setAttribute(Qt::AA_UseHighDpiPixmaps);
 #endif
+#if QT_VERSION >= 0x050600
+    QGuiApplication::setAttribute(Qt::AA_EnableHighDpiScaling);
+#endif
 #ifdef Q_OS_MAC
     QApplication::setAttribute(Qt::AA_DontShowIconsInMenus);
 #endif