Do not use parallelForEach to call maybeCompress().
Do not use parallelForEach to call maybeCompress().

Currently LLVM's paralellForEach has a problem with reentracy.
That caused https://bugs.llvm.org/show_bug.cgi?id=35788 (lld somtimes
hangs while linking Ruby 2.4) because maybeCompress calls writeTo which
uses paralellForEach.

This patch is to avoid using paralellForEach to call maybeCompress
to workaround the issue.

git-svn-id: f6089bf0e6284f307027cef4f64114ee9ebb0424@322041 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/lld,llvm-mirror/lld