[ASTImporter] Add test for C++'s try/catch statements.

Summary: Also enable exceptions in clang-import-test so that we can parse the test files.

Reviewers: a.sidorin, a_sidorin

Reviewed By: a_sidorin

Subscribers: a_sidorin, martong, cfe-commits

Differential Revision: https://reviews.llvm.org/D50978

llvm-svn: 340220