initial support for checking format strings, patch by Ted Kremenek:

initial support for checking format strings, patch by Ted Kremenek:

"I've coded up some support in clang to flag warnings for non-constant format strings used in calls to printf-like functions (all the functions listed in "man fprintf").  Non-constant format strings are a source of many security exploits in C/C++ programs, and I believe are currently detected by gcc using the flag -Wformat-nonliteral."

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@41003 91177308-0d34-0410-b5e6-96231b3b80d8