[Driver] Add PPC64 as supported for Scudo

Summary:
Scudo works on PPC64 as is, so mark the architecture as supported for it. This
will also require a change to config-ix.cmake on the compiler-rt side.

Update the tests accordingly.

Reviewers: eugenis, alekseyshl

Reviewed By: alekseyshl

Subscribers: cfe-commits

Differential Revision: https://reviews.llvm.org/D48833

llvm-svn: 336202