stub out demon/fontprovider so we can build debugger

src/font_provider/font_provider_inc.c

@@ -5,6 +5,8 @@
 
 #if FP_BACKEND == FP_BACKEND_DWRITE
 # include "dwrite/font_provider_dwrite.c"
+#elif FP_BACKEND == FP_BACKEND_FREETYPE
+# include "freetype/font_provider_freetype.c"
 #else
 # error Font provider backend not specified.
 #endif