Msan, fixing DTLS_on_tls_get_addr signature empty implementation

Summary: No supported oses normally compiled that code (or not for a long time) probably never caught it.

Patch by: David CARLIER

Reviewers: vitalybuka, krytarowski

Reviewed By: vitalybuka

Subscribers: kubamracek, llvm-commits, #sanitizers

Differential Revision: https://reviews.llvm.org/D43502

llvm-svn: 325664