Teach lit to expand glob expressions.

Teach lit to expand glob expressions.

This will enable removing hacks throughout the codebase
in clang and compiler-rt that feed multiple inputs to a
testing utility by globbing, all of which are either disabled
on Windows currently or using xargs / find hacks.

Differential Revision: https://reviews.llvm.org/D30380

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@296904 91177308-0d34-0410-b5e6-96231b3b80d8