Add a new compiler warning, which flags anti-patterns used as the size
argument in strncat.

The warning is ignored by default since it needs more qualification. 

TODO: The warning message and the note are messy when
strncat is a builtin due to the macro expansion.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@149524 91177308-0d34-0410-b5e6-96231b3b80d8
7 files changed