The test cases were crashing due to the mixed usage of the unwinding
functions from both libunwind and libgcc_s. The unwind functions are
mixed because the "llvm_unwinder" entry is not available in the
lit.site.cfg for libc++. As a result, "-lgcc_s" is picked instead of
"-lunwind". The extra option to lit --param=link_flags="-lunwind" won't
help either.
This CL fix the problem by adding llvm_unwinder to lit.site.cfg.in.
git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@237518 91177308-0d34-0410-b5e6-96231b3b80d8
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