[CStringSyntaxChecker] Check strlcat sizeof check

- Assuming strlcat is used with strlcpy we check as we can if the last argument does not equal os not larger than the buffer.
- Advising the proper usual pattern.

Reviewers: NoQ, george.karpenkov

Reviewed By: george.karpenkov

Differential Revision: https://reviews.llvm.org/D49722

llvm-svn: 339641