Add interceptors for the strtoi(3)/strtou(3) from NetBSD

Summary:
strtoi/strtou converts string value to an intmax_t/uintmax_t integer.

Add a dedicated test.

Enable this API for NetBSD.

It's a reworked version of the original work by Yang Zheng.

Reviewers: joerg, vitalybuka

Reviewed By: vitalybuka

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

Tags: #sanitizers

Differential Revision: https://reviews.llvm.org/D54702

llvm-svn: 348663