[asan] Interceptors for Fuchsia

Summary:
Fuchsia uses the "memintrinsics" interceptors, though not via any
generalized interception mechanism.  It doesn't use any other interceptors.

Submitted on behalf of Roland McGrath.

Reviewers: vitalybuka, alekseyshl, kcc

Reviewed By: vitalybuka

Subscribers: kubamracek, phosek, filcab, llvm-commits

Tags: #sanitizers

Differential Revision: https://reviews.llvm.org/D36189

llvm-svn: 309798