This patch adds a `check-cxx-abilist` target which verifies the libc++.so ABI
when the current build configuration matches the configuration used to generate
the ABI lists.
In order to make this change `HandleOutOfTreeLLVM.cmake` needed to be modified
to include `LLVMConfig.cmake` so that `TARGET_TRIPLE` is defined. Hopefully
the changes needed to accommodate this won't break existing build
configurations.
git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@286789 91177308-0d34-0410-b5e6-96231b3b80d8
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