[DAG] Change isGCValue detection for statepoint lowering

[DAG] Change isGCValue detection for statepoint lowering

isGCValue should detect whether the deopt value is a GC pointer.
Currently it checks by finding the value in SI.Bases and SI.Ptrs.
However these data structures contain only those values which
have corresponding gc.relocate call. So we can miss GC value if it
does not have gc.relocate call (dead after the call).

Check GC strategy whether pointer is GC one or consider any pointer
to be GC one conservatively.

Reviewers: reames, dantrushin
Reviewed By: reames
Subscribers: hiraditya, llvm-commits
Differential Revision: https://reviews.llvm.org/D77130