Hoist LLVM's lit testsuite infrastructure into module so that it can be

Hoist LLVM's lit testsuite infrastructure into module so that it can be
re-used. Also, build in direct support for accumulating a set of lit
parameters, arguments, and testsuites to run as part of a 'check-all'
rule. This sinks 'check-all' from a Clang-specific construct to
a generic construct of the project.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@159482 91177308-0d34-0410-b5e6-96231b3b80d8