A client of a header that relies on ABI breaking should get the macro
exported there.
Before this, the unittest for Support/Error including Support/Error.h
didn't get the macro exported by the Support module, because the
latter only re-export its submodules and included module, not
textual headers.
Hopefully, it'll also fix the build with local submodule visibility,
since the LLVM_Utils contains two submodules: ADT and Support. They
both include abi-breaking.h that defines a symbol. The textual
inclusion lead to a double definition of the symbol which broke
the parent module.
Differential Revision: https://reviews.llvm.org/D27273
llvm-svn: 288400
