A hack to make -dynamic work again:
when a library listed in extraLibraries ends with "_cbits", append "_dyn"
when -dynamic is passed, i.e. extraLibraries = ["foo", "HSbase_cbits"]
loads -lfoo and -lHSbase_cbits in the static case, but -lfoo and
-lHSbase_cbits_dyn in the -dynamic case.

It's an ugly hack, but it affects only the case when -dynamic is passed,
which would not work otherwise right now, so let's

MERGE TO STABLE