[GlobalISel][InstructionSelect] Making Coverage Info generation optional on per-match table basis
to make sure that Testgen always has access to coverage info even if
the match table used by the selector itself is stripped off that
information for performance reasons.
Reviewers: dsanders, aemerson
Reviewed By: dsanders
Subscribers: rovka, kristof.beyls, llvm-commits, dsanders
Differential Revision: https://reviews.llvm.org/D46098