In certain configurations, libc++ headers all exist in the same directory, and libc++ binaries exist in the same directory as lldb libs. When `LLVM_ENABLE_PER_TARGET_RUNTIME_DIR` is enabled (*and* the host is not Apple, which is why I assume this wasn't caught by others?), this is not the case: most headers will exist in the usual `include/c++/v1` directory, but `__config_site` exists in `include/$TRIPLE/c++/v1`. Likewise, the libc++.so binary exists in `lib/$TRIPLE/`, not `lib/` (where LLDB libraries reside).
This also adds the just-built-libcxx functionality to the lldb-dotest tool.
The `LIBCXX_` cmake config is borrowed from `libcxx/CMakeLists.txt`. I could not figure out a way to share the cmake config; ideally we would reuse the same config instead of copy/paste.
Reviewed By: JDevlieghere, fdeazeve
Differential Revision: https://reviews.llvm.org/D133973
cb0eb9d8dd