[scudo] Pass SANITIZER_COMMON_LINK_FLAGS to the shared library LINK_FLAGS

Summary:
We somehow never did it, and it raised no issue until now, when trying to
enable Fuchsia as a supported Scudo platform in the cmake config.

So propagate SANITIZER_COMMON_LINK_FLAGS for now.

Reviewers: alekseyshl, flowerhack

Reviewed By: flowerhack

Subscribers: mgorny, #sanitizers, llvm-commits

Differential Revision: https://reviews.llvm.org/D42314

llvm-svn: 322999