make the testsuite work with THREADS=2
The testsuite driver supports THREADS=2, unfortunately there are a few sequencing dependencies in the tests themselves which means that you may get false failures, depending on the order in which the tests are run.
These are the tests I know about that fail in this way:
cabal01(normal)
ffi018(normal)
mod144(normal)
mod158(normal)
mod166(normal)