We want to move functionality from the LLVM ORCTargetProcess library into the
ORC runtime, and this will mean implementing remote-executor testing tools
(like llvm-jitlink-executor and lli-child-target) in the ORC runtime.
This patch refactors the ORC runtime build system to introduce an
add_orc_tool function that can be used to add new test tools. The code is
modeled on existing functions for adding unit tests.
A placeholder orc-rt-executor tool and test are added to verify that the
config changes behave as expected.
Reviewed By: phosek
Differential Revision: https://reviews.llvm.org/D133084
