C99 DR #316 implies that the function parameter types that are known

C99 DR #316 implies that the function parameter types that are known
only from a function definition (that does not have a prototype) are
only used to determine the compatible with other declarations of that
same function. In particular, when referencing the function we pretend
as if it does not have a prototype. Implement this behavior, which
fixes PR3626.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@65460 91177308-0d34-0410-b5e6-96231b3b80d8