Add new interceptors for vis(3) API in NetBSD

Summary:
Add interceptors for the NetBSD style of vis(3) present inside libc:

 - vis
 - nvis
 - strvis
 - stravis
 - strnvis
 - strvisx
 - strnvisx
 - strenvisx
 - svis
 - snvis
 - strsvis
 - strsnvis
 - strsvisx
 - strsnvisx
 - strsenvisx
 - unvis
 - strunvis
 - strnunvis
 - strunvisx
 - strnunvisx

Add a dedicated test verifying the installed interceptors.

Based on original work by Yang Zheng.

Reviewers: vitalybuka, joerg

Reviewed By: vitalybuka

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

Tags: #sanitizers

Differential Revision: https://reviews.llvm.org/D54594

llvm-svn: 349018