Add a new clang-tidy module for Fuchsia as an umbrella to diagnose issues with...

Add a new clang-tidy module for Fuchsia as an umbrella to diagnose issues with the Fuschia and Zircon coding guidelines (https://fuchsia.googlesource.com/zircon/+/master/docs/cxx.md). Adds the first of such checkers, which detects when default arguments are declared in a function declaration or when default arguments are used at call sites.

Patch by Julie Hockett

llvm-svn: 319225