[IR] Add additional addParamAttr/removeParamAttr to AttributeList API

Summary:
Fairly straightforward patch to fill in some of the holes in the
attributes API with respect to accessing parameter/argument attributes.
The patch aims to step further towards encapsulating the
idx+FirstArgIndex pattern to access these attributes to within the
AttributeList.

Patch by Daniel Neilson!

Reviewers: rnk, chandlerc, pete, javed.absar, reames

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D33355

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@304329 91177308-0d34-0410-b5e6-96231b3b80d8
8 files changed