dispserv_win32: define _WIN32_WINNT before including Windows headers

Fixes "Set Display-Reported Refresh Rate" reporting 0.000 Hz on Windows
nightly builds (compiled with MinGW/GCC 10.2.0) while working correctly
on builds compiled with newer toolchains (MinGW/GCC 15.2.0).

win32_display_server_get_refresh_rate() guards its QueryDisplayConfig
implementation with `#if _WIN32_WINNT >= 0x0601`, falling back to
`return 0.0f` otherwise. The file already attempted to define
_WIN32_WINNT to 0x0601 when undefined, but the fallback #define was
placed *after* <objbase.h>, <initguid.h>, <windows.h>, <ntverp.h> and
<shlobj.h>, by which point the SDK headers had already locked in the
toolchain's default value. Older mingw-w64 runtimes default to a value
below 0x0601 when the build system does not specify one, so the
function was compiled to unconditionally return 0.0f. Newer mingw-w64
runtimes default to 0x0A00, which is why the issue did not reproduce
locally.

Move the _WIN32_WINNT (and _WIN32_WINDOWS) fallback defines to the top
of the translation unit, before any Windows headers are included, so
the version gate is honored regardless of toolchain.

Author: LibretroAdmin

gfx/display_servers/dispserv_win32.c

@@ -17,6 +17,15 @@
 
 #define WIN32_LEAN_AND_MEAN
 
+/* Must be defined BEFORE any Windows headers are pulled in, otherwise
+ * the SDK locks in the toolchain default (which on older mingw-w64
+ * runtimes is below 0x0601), and the QueryDisplayConfig code path in
+ * win32_display_server_get_refresh_rate() gets compiled out, returning
+ * a hardcoded 0.0f. */
+#ifndef _WIN32_WINDOWS
+#define _WIN32_WINDOWS 0x0601
+#endif
+
 /* VC6 needs objbase included before initguid, but nothing else does */
 #include <objbase.h>
 #include <initguid.h>