[RS4GC] Use "deopt" operand bundles

Summary:
This is a step towards using operand bundles to carry deopt state till
RewriteStatepointsForGC.  The change adds a flag to
RewriteStatepointsForGC that teaches it to pick up deopt state from a
`"deopt"` operand bundle attached to the `call` or `invoke` it is
wrapping.

The command line flag added, `-rs4gc-use-deopt-bundles`, will only exist
for a short while.  Once we are able to pipe deopt bundle state through
the full optimization pipeline without problems, we will "constant fold"
`-rs4gc-use-deopt-bundles` to `true`.

Reviewers: swaroop.sridhar, reames

Subscribers: llvm-commits, sanjoy

Differential Revision: http://reviews.llvm.org/D13372

llvm-svn: 250489