ImFileOpen: MinGW uses _wfopen() codepath to support UTF-8 filenames (#917)

imgui.cpp

@@ -1295,7 +1295,7 @@ void ImGui::ColorConvertHSVtoRGB(float h, float s, float v, float& out_r, float&
 
 FILE* ImFileOpen(const char* filename, const char* mode)
 {
-#ifdef _MSC_VER
+#if defined(_WIN32) && !defined(__CYGWIN__)
     // We need a fopen() wrapper because MSVC/Windows fopen doesn't handle UTF-8 filenames. Converting both strings from UTF-8 to wchar format (using a single allocation, because we can)
     const int filename_wsize = ImTextCountCharsFromUtf8(filename, NULL) + 1;
     const int mode_wsize = ImTextCountCharsFromUtf8(mode, NULL) + 1;