[LLDB][PPC64] Fix TestGdbRemoteAuxvSupport

Summary: PPC64's auxvec has a special key that must be ignored.

Reviewers: clayborg, labath

Reviewed By: clayborg, labath

Subscribers: alexandreyy, lbianc

Differential Revision: https://reviews.llvm.org/D43771
Patch by Leandro Lupori <leandro.lupori@gmail.com>.

llvm-svn: 328486