See attachments.
Created attachment 17832 [details] Compile error messages
Created attachment 17833 [details] Portage info
Matthew, please re-emerge fontconfig.
Yes, please emerge fontconfig and report back if this fixes things.
Now there are different errors... Error log to follow.
Created attachment 17882 [details] Compile Errors part 2
Try with USE="-nls"? This looks like an upstream bug, but this might be a temporary work-around.
If I use -nls, I get the first batch of errors [1st attachment].
I cant confirm this, it builds for me and lots of others..