build: Bump minimum Qt version to 5.9.5

Author: hebasto

configure.ac

@@ -1283,7 +1283,7 @@ else
   BITCOIN_QT_INIT
 
   dnl sets $bitcoin_enable_qt, $bitcoin_enable_qt_test, $bitcoin_enable_qt_dbus
-  BITCOIN_QT_CONFIGURE([5.5.1])
+  BITCOIN_QT_CONFIGURE([5.9.5])
 
   dnl Keep a copy of the original $QT_INCLUDES and use it when invoking qt's moc
   QT_INCLUDES_UNSUPPRESSED=$QT_INCLUDES

doc/dependencies.md

@@ -21,7 +21,7 @@ These are the dependencies currently used by Bitcoin Core. You can find instruct
 | PCRE |  |  |  |  | [Yes](https://github.com/bitcoin/bitcoin/blob/master/depends/packages/qt.mk) |
 | Python (tests) |  | [3.6](https://www.python.org/downloads) |  |  |  |
 | qrencode | [3.4.4](https://fukuchi.org/works/qrencode) |  | No |  |  |
-| Qt | [5.9.8](https://download.qt.io/official_releases/qt/) | [5.5.1](https://github.com/bitcoin/bitcoin/issues/13478) | No |  |  |
+| Qt | [5.9.8](https://download.qt.io/official_releases/qt/) | [5.9.5](https://github.com/bitcoin/bitcoin/issues/20104) | No |  |  |
 | SQLite | [3.32.1](https://sqlite.org/download.html) | [3.7.17](https://github.com/bitcoin/bitcoin/pull/19077) |  |  |  |
 | XCB |  |  |  |  | [Yes](https://github.com/bitcoin/bitcoin/blob/master/depends/packages/qt.mk) (Linux only) |
 | xkbcommon |  |  |  |  | [Yes](https://github.com/bitcoin/bitcoin/blob/master/depends/packages/qt.mk) (Linux only) |

src/qt/bitcoin.cpp

@@ -464,9 +464,7 @@ int GuiMain(int argc, char* argv[])
 
     // Generate high-dpi pixmaps
     QApplication::setAttribute(Qt::AA_UseHighDpiPixmaps);
-#if QT_VERSION >= 0x050600
     QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);
-#endif
 
 #if (QT_VERSION <= QT_VERSION_CHECK(5, 9, 8)) && defined(Q_OS_MACOS)
     const auto os_name = QSysInfo::prettyProductName();