[ExpressionParser] Add swift-lldb case for finding clang resource dir

Summary:
I'm adding this to reduce the difference between swift-lldb and
llvm.org's lldb.

Reviewers: aprantl, davide, compnerd, JDevlieghere, jingham

Subscribers: lldb-commits

Differential Revision: https://reviews.llvm.org/D59708

llvm-svn: 357030