Summary: Modify the test infrastructure to properly handle tests that require z3, and merge together the output of all tests on success. This is required for D28954.

Reviewers: dcoughlin, zaks.anna, NoQ, xazax.hun

Subscribers: cfe-commits

Differential Revision: https://reviews.llvm.org/D33308

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@305480 91177308-0d34-0410-b5e6-96231b3b80d8