graphics/agg: Mark BROKEN, fails to build with freetype2 2.13.3

Fails with the following error:
agg_font_freetype.cpp:189:35: error: assigning to 'char *' from 'unsigned char *' converts between pointers to integer types where one is of the unique plain 'char' type and the other is not

PR: 281321
Approved by: bofh (maintainer)