-g, by reverting r219139. The LLVM PR referenced in that revision was
fixed in the mean time, and we imported a clang snapshot soon
afterwards, so the temporary workaround of disabling clang's integrated
assembler is no longer needed.
In this particular case, using e.g. DEBUG_FLAGS=-g causes clang to
output certain directives into assembly that our version of GNU as
chokes on.
Reported by: dougb
Approved by: re (kib)