[sanitizer_common] Add SANITIZER_FUCHSIA

Summary: More changes to follow will add the Fuchsia port.

Submitted on behalf of Roland McGrath.

Reviewers: vitalybuka, alekseyshl, kcc

Reviewed By: vitalybuka

Subscribers: kubamracek, llvm-commits, phosek, filcab

Tags: #sanitizers

Differential Revision: https://reviews.llvm.org/D36027

llvm-svn: 309539