Fix `-no_compact_unwind` check
N.B. During development in !9263 (merged) we came across multiple tasks and bugs regarding the configuration script. In preparation of merging it, we're opening tickets for the leftover tasks both regarding the new
ghc-toolchain and the toolchain logic in configure. This is one of those tickets.
ghc-toolchain we noticed that the
FP_PROG_LD_NO_COMPACT_UNWIND check is subtly wrong. Specifically, we pass
ld.gold interprets this as
-n o_compact_unwind, which is a valid argument.
We should just make this check specific to Darwin (and mirror this change in