Otherwise when we visit all libcalls in
updateCGAndAnalysisManagerForPass(), the old libcall is dead and doesn't
have a node.
We treat libcalls conservatively in LazyCallGraph because any function
may introduce calls to them out of thin air.
It is weird to change the signature of a libcall since introducing calls
to the libcall with a different signature may break, but other passes
like deadargelim already do it, so let's preserve this behavior for now.
Fixes an issue found in D128830.
Reviewed By: psamolysov
Differential Revision: https://reviews.llvm.org/D132764
Arthur Eubanks