2.0 frontend hangs

Hello, Bram.

How should I debug the frontend (currently recompiling with debugging
support), as there are various threads/processes involved? Should I
file a bug report?

First of all, provide -v option to llvm-gcc. This will enable "verbose"
output and, actually, will show you the exact command line of the tool
executed.
Second, determine the tool, arguments supplied, source files, etc. And
try to reproduce the hang just running the tool "by hands". After you
can submit bug report, which can be possible reproducible.

PS: I'm trying ioquake3 on my linux box.