[clang-tidy] add check cppcoreguidelines-pro-type-vararg

Summary:
This check flags all calls to c-style vararg functions and all use
of va_list, va_start and va_arg.

Passing to varargs assumes the correct type will be read. This is
fragile because it cannot generally be enforced to be safe in the
language and so relies on programmer discipline to get it right.

This rule is part of the "Type safety" profile of the C++ Core
Guidelines, see
https://github.com/isocpp/CppCoreGuidelines/blob/master/CppCoreGuidelines.md#-type8-avoid-reading-from-varargs-or-passing-vararg-arguments-prefer-variadic-template-parameters-instead

This commits also reverts
  "[clang-tidy] add cert's VariadicFunctionDefCheck as cppcoreguidelines-pro-type-vararg-def"
because that check makes the SFINAE use of vararg functions impossible.

Reviewers: alexfh, sbenza, bkramer, aaron.ballman

Subscribers: cfe-commits

Differential Revision: http://reviews.llvm.org/D13787

llvm-svn: 250939