[IR] Use LLVM_ENABLE_ABI_BREAKING_CHECKS to guard ABI changes.

Incorrect usage of NDEBUG to guard ABI changes can prevent clients
from enabling assertions for their C++ code while having assertions in
LLVM turned off. So we use LLVM_ENABLE_ABI_BREAKING_CHECKS instead, as
described in llvm/docs/ProgrammersManual.rst. Most types already use this
macro, however, there were a couple of stragglers in ValueHandle.h, which
are fixed by this revision.

Reviewed By: dblaikie, dexonsmith

Differential Revision: https://reviews.llvm.org/D93433