Add new interceptor: strmode(3)

Summary:
strmode - convert inode status information into a symbolic string

Sponsored by <The NetBSD Foundation>

Reviewers: joerg, vitalybuka

Reviewed By: vitalybuka

Subscribers: kubamracek, llvm-commits, #sanitizers

Tags: #sanitizers

Differential Revision: https://reviews.llvm.org/D43485

llvm-svn: 325588