Add a new clang-tidy checker that flags throw expressions whose thrown type is...

Add a new clang-tidy checker that flags throw expressions whose thrown type is not nothrow copy constructible. While the compiler is free to elide copy constructor calls in some cases, it is under no obligation to do so, which makes the code a portability concern as well as a security concern.

This checker corresponds to the CERT secure coding rule: https://www.securecoding.cert.org/confluence/display/cplusplus/ERR60-CPP.+Exception+objects+must+be+nothrow+copy+constructible

llvm-svn: 253246