Merge bitcoin-core/gui#755: Silence `-Wcast-function-type` warning

befb42f146 qt: Silence `-Wcast-function-type` warning (Hennadii Stepanov)

Pull request description:

  On Fedora 38 @ 8f7b9eb8711fdb32e8bdb59d2a7462a46c7a8086:
  ```
  $ x86_64-w64-mingw32-g++ --version | head -1
  x86_64-w64-mingw32-g++ (GCC) 12.2.1 20221121 (Fedora MinGW 12.2.1-8.fc38)
  $ ./configure CONFIG_SITE=$PWD/depends/x86_64-w64-mingw32/share/config.site CXXFLAGS="-Wno-return-type -Wcast-function-type"
  $ make > /dev/null
  qt/winshutdownmonitor.cpp: In static member function 'static void WinShutdownMonitor::registerShutdownBlockReason(const QString&, HWND__* const&)':
  qt/winshutdownmonitor.cpp:46:42: warning: cast between incompatible function types from 'FARPROC' {aka 'long long int (*)()'} to 'PSHUTDOWNBRCREATE' {aka 'int (*)(HWND__*, const wchar_t*)'} [-Wcast-function-type]
     46 |     PSHUTDOWNBRCREATE shutdownBRCreate = (PSHUTDOWNBRCREATE)GetProcAddress(GetModuleHandleA("User32.dll"), "ShutdownBlockReasonCreate");
        |                                          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  ```

  [Required](https://github.com/bitcoin/bitcoin/pull/25972#issuecomment-1713999563) for https://github.com/bitcoin/bitcoin/pull/25972.

  Picked from https://trac.nginx.org/nginx/ticket/1865.

ACKs for top commit:
  MarcoFalke:
    review ACK befb42f146

Tree-SHA512: b37b2c5dd8702caf84d1833c3511bc46ee14f23b84678b8de0fd04e24e5ecc5fd4d27ba38be0d0b08de91299369f70d4924c895a71fd8e0b6feffcfb7407574a

src/qt/winshutdownmonitor.cpp

@@ -43,7 +43,7 @@ bool WinShutdownMonitor::nativeEventFilter(const QByteArray &eventType, void *pM
 void WinShutdownMonitor::registerShutdownBlockReason(const QString& strReason, const HWND& mainWinId)
 {
     typedef BOOL (WINAPI *PSHUTDOWNBRCREATE)(HWND, LPCWSTR);
-    PSHUTDOWNBRCREATE shutdownBRCreate = (PSHUTDOWNBRCREATE)GetProcAddress(GetModuleHandleA("User32.dll"), "ShutdownBlockReasonCreate");
+    PSHUTDOWNBRCREATE shutdownBRCreate = (PSHUTDOWNBRCREATE)(void*)GetProcAddress(GetModuleHandleA("User32.dll"), "ShutdownBlockReasonCreate");
     if (shutdownBRCreate == nullptr) {
         qWarning() << "registerShutdownBlockReason: GetProcAddress for ShutdownBlockReasonCreate failed";
         return;