swift234

[test] Throw away logic for detecting LLVM build directories.

We were never in this situation. For future reference, there are
two ways to use lit manually:

% lit.py $BUILD/swift*/test-macosx-x86_64/$TESTS
% lit.py --param swift_site_config=$BUILD/swift*/test-macosx-x86_64/lit.site.cfg test/$TESTS

The latter is more verbose, but lets you point at real test files in the
source directory instead of pretending they exist in the build directory.
There are probably still further improvements to be made here.

(P.S. I suggest using -sv if running lit from the command line.)

Swift SVN r31647