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.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@294861 91177308-0d34-0410-b5e6-96231b3b80d8