Parallel builds fail in mysterious ways

[shish]

I want to create debug and release builds (and a few other combinations of flags) at the same time - running multiple instances of nimble build in the same directory at the same time results in a variety of fun and mysterious errors, but running in serial works fine.

eg:

lto1: internal compiler error: unexpected file name /home/dev/.cache/nim/rosettaboy_r/@mcart.nim.c. in linker resolution file. Expected /home/dev/.cache/nim/rosettaboy_r/@mcpu.nim.c.o

Ideally I'd love a way to specify separate source code / build temp / build output directories, but I'd also be happy if nimble just created a lockfile in the current directory and had multiple instances form a queue to avoid breaking :)