Add new interceptors: strlcpy(3) and strlcat(3)

Summary:
NetBSD ships with strlcpy(3) and strlcat(3), a safe
replacement of strcpy(3) and strcat(3).

Hide both functions under SANITIZER_INTERCEPT_STRLCPY.

Sponsored by <The NetBSD Foundation>

Reviewers: joerg, vitalybuka

Reviewed By: vitalybuka

Subscribers: llvm-commits, kubamracek, #sanitizers

Tags: #sanitizers

Differential Revision: https://reviews.llvm.org/D42061

llvm-svn: 324034