The last argument is expected to be the destination buffer size (or less).
Detects if it points to destination buffer size directly or via a variable.
Detects if it is an integral, try to detect if the destination buffer can receive the source length.
Updating bsd-string.c unit tests as it make it fails now.
Reviewers: george.karpenpov, NoQ
Reviewed By: george.karpenkov
Differential Revision: https://reviews.llvm.org/D48884
git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@337499 91177308-0d34-0410-b5e6-96231b3b80d8