Put ABI breaking test in Error checking behind LLVM_ENABLE_ABI_BREAKING_CHECKS

This macro is supposed to be the one controlling the compatibility
of ABI breaks induced when enabling or disabling assertions in LLVM.

The macro is enabled by default in assertions build, so this commit
won't disable the tests.

Differential Revision: https://reviews.llvm.org/D26700

llvm-svn: 288087