The DwarfLinker can have some very deep recursion that can max out the
(significantly smaller) stack when using threads. We don't want this
limitation when we only have a single thread. We already have this
workaround for the architecture-related threading. This patch applies
the same workaround to the parallel analysis and cloning.
Differential revision: https://reviews.llvm.org/D45172
llvm-svn: 329093