Install a cmake config file. Copied exactly from how clang exports.
I'm slightly confused since it looks like the build is manually
generating a very similar *Targets.cmake to what gets auto-generated
by export(). After generating the build, I see:
build/tools/lld/cmake/modules/CMakeFiles/Export/lib/cmake/lld/LLDTargets.cmake build/lib/cmake/lld/LLDTargets.cmake build/tools/clang/cmake/modules/CMakeFiles/Export/lib/cmake/clang/ClangTargets.cmake build/lib/cmake/clang/ClangTargets.cmake
The cmake generated one "wins" and is what I see in the installed
tree. I'm guessing this is somehow for the benefit of old versions
I also wasn't sure whether the canonical capitalization is "lld" or
"LLD". The project() is still calling this lld, but most places seemed
to capitalize it.