MesaLib/llvm trouble?

[Greg tTroxel <gdt%lexort.com@localhost>]

I am not clear on the details, but from a recent bulk build report, it
seems MesaLib is not building, and this is probably related to a recent
libLLVM update.  With any luck I'm just confused and things are fine,
but given that we are heading for a freeze I wanted to ask sooner rather
than later.

Can someone explain precisely what's going on, and a suggested way
forward?