Change the wording of RTTI errors to make them more generic.

An attempt to use dynamic_cast while rtti is disabled, used to emit the error:

  cannot use dynamic_cast with -fno-rtti

and a similar one for typeid.

This patch changes that to:

  use of dynamic_cast requires -frtti

Differential Revision: https://reviews.llvm.org/D47291

llvm-svn: 334153