[ubsan] Introduce %clangxx substitution for all C++ tests.

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@193059 91177308-0d34-0410-b5e6-96231b3b80d8
Runtime support for the indirect function call checker.

Differential Revision: http://llvm-reviews.chandlerc.com/D1339

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@193060 91177308-0d34-0410-b5e6-96231b3b80d8