Reland "[lit] Adding config initialization to lit tests in clang-tools-extra"

Adding the config initialization to clang-tools-extra so that tests that
use REQUIRES, UNSUPPORTED, and XFAIL based on platform or target triple
work properly.

git-svn-id: https://llvm.org/svn/llvm-project/clang-tools-extra/trunk@328131 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed