[clang-tidy] add IgnoreMacros option to readability-redundant-smartptr-get

And also enable it by default to be consistent with e.g. modernize-use-using.

This helps e.g. when running this check on client code where the macro is
provided by the system, so there is no easy way to modify it.

Reviewed By: JonasToth

Differential Revision: https://reviews.llvm.org/D53454

llvm-svn: 344871