Add new interceptor: fgetln(3)

Summary:
fgetln - get a line from a stream

Sponsored by <The NetBSD Foundation>

Reviewers: vitalybuka, joerg

Reviewed By: vitalybuka

Subscribers: llvm-commits, kubamracek, #sanitizers

Tags: #sanitizers

Differential Revision: https://reviews.llvm.org/D43482

llvm-svn: 325587