[llvm] Reapply "[llvm-jitlink] Use concurrent linking by default." with fixes. (PR #120958)

[NAKAMURA Takumi via llvm-commits]

chapuni wrote:

@lhames Looks like this triggered occasional failures, possibly due to interrupted messages by insufficient locks.

https://lab.llvm.org/buildbot/#/builders/174/builds/10572
https://lab.llvm.org/buildbot/#/builders/76/builds/5597
https://lab.llvm.org/buildbot/#/builders/76/builds/5599
https://lab.llvm.org/buildbot/#/builders/140/builds/13674 (and more)
https://lab.llvm.org/buildbot/#/builders/137/builds/10828

https://github.com/llvm/llvm-project/pull/120958