Summary:
This is an alternative solution to running the lit test suite on bots
without polluting the source directory. Each input test suite gets an
auto-generated site config in the build directory that points back to
the test input source directory.
This adds some cmake comlexity, but now we don't need to remove and
re-copy the test input directory before every test.
Reviewers: delcypher, modocache
Subscribers: mgorny, llvm-commits
Differential Revision: https://reviews.llvm.org/D36026
llvm-svn: 309602
