Add new interceptor for regex(3) in NetBSD

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

 - regcomp
 - regexec
 - regerror
 - regfree
 - regnsub
 - regasub

Add a dedicated test verifying the installed interceptors.

Reviewers: vitalybuka, joerg

Reviewed By: vitalybuka

Subscribers: kubamracek, llvm-commits, mgorny, #sanitizers

Tags: #sanitizers

Differential Revision: https://reviews.llvm.org/D54584

llvm-svn: 348224