Adding a checker (cert-dcl50-cpp) that detects the definition of a C-style...

Adding a checker (cert-dcl50-cpp) that detects the definition of a C-style variadic function in C++ code. Corresponds to the CERT C++ secure coding rule: https://www.securecoding.cert.org/confluence/display/cplusplus/DCL50-CPP.+Do+not+define+a+C-style+variadic+function

llvm-svn: 249343