Strip unknown/unsupported attributes (like readnone/readonly for parameters).

Bug: 12135682

Jellybean's LLVM version didn't support readnone/readonly as anything
other than function attributes, so it will fail verification otherwise.
Since we never ran the verifier in Jellybean, it ends up with potential
crashes deeper in CodeGen.

Change-Id: I0a93a548b427f610fa9ca0a1ae0b432e6fa39e11
4 files changed