Extended Description

It started failing since r323450, but that's only because it did not actually use modules before that.

This error message may be an indication of the problem:

error: B-1GM9AHXMM9U5Y.pcm DWARF DIE at 0x00000033 (class Module) has a member variable 0x0000003c (MBptr) whose type is a forward declaration, not a complete definition.
Try compiling the source file with -fstandalone-debug

The -fstandalone-debug is a red herring because we already pass that flag.