Add new interceptor for getmntinfo(3) from NetBSD

Summary:
getmntinfo gets information about mounted file systems.

Add a dedicated test for new interceptor.

Based on original work by Yang Zheng.

Reviewers: joerg, vitalybuka

Reviewed By: vitalybuka

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

Tags: #sanitizers

Differential Revision: https://reviews.llvm.org/D54611

llvm-svn: 347083