Add interceptor for the setvbuf(3) from NetBSD

Summary:
setvbuf(3) is a routine to setup stream buffering.

Enable the interceptor for NetBSD.

Add dedicated tests for setvbuf(3) and functions
on top of this interface: setbuf, setbuffer, setlinebuf.

Based on original work by Yang Zheng.

Reviewers: joerg, vitalybuka

Reviewed By: vitalybuka

Subscribers: devnexen, tomsun.0.7, kubamracek, llvm-commits, mgorny, #sanitizers

Tags: #sanitizers

Differential Revision: https://reviews.llvm.org/D54548

llvm-svn: 347270