[ORC] Update the GlobalMappingLayer interface to fit the error-ized layer
concept.

Add a unit-test to make sure we don't backslide, and tweak the MockBaseLayer
utility to make it easier to test this kind of thing in the future.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@314374 91177308-0d34-0410-b5e6-96231b3b80d8
4 files changed