We can't exit early when on error here as some threads may still be holding
references to LookupMutex.

Since we don't need high performance in the error case the easy solution is to
drop the early-exit in the error case and wait for all tasks to complete before
returning the error.

Thanks to Jameson Nash for spotting this bug!

This reapplies b0979b8c65d, which was reverted in 370aecb9572 due to bot
failures. The failures were caused by typos in the testcase that are fixed in
this patch.

Broke buildbots: https://lab.llvm.org/buildbot/#/builders/10/builds/5025

This reverts commit b0979b8c65d76cc1897e97b9ad091d8d99abdd18.

The context string can be added to indicate the source of the duplicate
definition. E.g. if the context is set to "foo2.o", then:

"Duplicate definition of symbol 'foo'"

becomes

"In foo2.o, duplicate definition of symbol 'foo'".

The JITDylib::defineImpl method is updated to use the name of the
MaterializationUnit being added as the context string for duplicate definition
errors. The JITDylib::defineMaterializing method is updated to use
"defineMaterializing operation" as the conext string.

We can use *Set::insert_range to collapse:

  for (auto Elem : Range)
    Set.insert(E);

down to:

  Set.insert_range(Range);

In some cases, we can further fold that into the set declaration.

Re-enables compact-unwind support in JITLink, which was reverted in b04847b427d
due to buildbot failures.

The underlying cause for the failures on the buildbots was the lack of
compact-unwind registration support on older Darwin OSes. Since the
CompactUnwindManager pass now removes eh-frames by default we were left with
unwind-info that could not be registered. On x86-64, where eh-frame info is
produced by default the solution is to fall back to using eh-frames. On arm64
we simply can't support exceptions on older OSes.

This patch updates the EHFrameRegistrationPlugin to remove the compact-unwind
section (__LD,__compact_unwind) when installed, forcing use of eh-frames when
the EHFrameRegistrationPlugin is used. In LLJIT, the EHFrameRegistrationPlugin
continues to be used for all non-Darwin platform, and will be added on Darwin
platforms when the a CompactUnwindRegistrationPlugin instance can't be created
(e.g. due to missing support for compact-unwind info registration).

The lit.cfg.py script is updated to check whether the host OSes default unwind
info supports JIT registration, allowing tests to be disabled for older Darwin
OSes on arm64.

This reverts commit d6524c8dfa37634257050ca71d16e117b802181c. This
reverts commit b1bd73700a1fb6f450e0f6f9c405a9c8bde2cae7.

This was causing bot failures on Darwin


https://green.lab.llvm.org/job/llvm.org/job/clang-stage1-cmake-RA-incremental/7315/
  Clang.Interpreter.simple-exception.cpp

Clang-Unit.Interpreter/ExceptionTests/_/ClangReplInterpreterExceptionTests/0.1
  LLVM.ExecutionEngine/OrcLazy.minimal-throw-catch.ll

https://green.lab.llvm.org/job/llvm.org/job/clang-stage1-RA/3415/
  ORC-x86_64-darwin.TestCases/Darwin/Generic.exceptions.cpp
  ORC-x86_64-darwin.TestCases/Darwin/x86-64.lljit-ehframe.cpp