Fix AAResults::callCapturesBefore for operand bundles

Summary:
AAResults::callCapturesBefore would previously ignore operand
bundles. It was possible for a later instruction to miss its memory
dependency on a call site that would only access the pointer through a
bundle.

Patch by Oscar Blumberg!

Reviewers: sanjoy

Differential Revision: http://reviews.llvm.org/D21286

llvm-svn: 272580