[clang-tidy] Adding Fuchsia checker for multiple inheritance

Adds a check to the Fuchsia module to warn when a class
inherits from multiple classes that are not pure virtual.

See https://fuchsia.googlesource.com/zircon/+/master/docs/cxx.md
for reference.

Differential Revision: https://reviews.llvm.org/D40580

llvm-svn: 323011