Also, fix a few other details of the cmake test target and rename it to
'check'. CMake tests now work for the most part, but there are a handful of
failures left due to missing site.exp bits.

llvm-svn: 86452

llvm-svn: 85614

llvm-svn: 81664

llvm-svn: 81427

 - This adds 'make check-lit' from the top-level Makefile.

llvm-svn: 81191