Bug 1533142 - followup: Fix Windows MinGW bustage. r=me

gfx/2d/ScaledFontDWrite.cpp

@@ -476,7 +476,7 @@ bool ScaledFontDWrite::GetWRFontInstanceOptions(
     std::vector<FontVariation>* aOutVariations) {
   wr::FontInstanceOptions options;
   options.render_mode = wr::ToFontRenderMode(GetDefaultAAMode());
-  options.flags = 0;
+  options.flags = wr::FontInstanceFlags{0};
   if (mFontFace->GetSimulations() & DWRITE_FONT_SIMULATIONS_BOLD) {
     options.flags |= wr::FontInstanceFlags_SYNTHETIC_BOLD;
   }