Attributes on K&R C functions should not cause incompatible function type with...

Attributes on K&R C functions should not cause incompatible function type with a redeclaration having the same attribute. Fixing this introduced a secondary problem where we were assuming that K&R functions could not be attributed types when reporting old-style function definitions that are not preceded by a prototype.

This patch fixes PR31020.

llvm-svn: 294861