Handle any undeclared parameters in a K&R-style function with a

Handle any undeclared parameters in a K&R-style function with a
special action, inside function prototype scope. This avoids confusion
when we try to inject these parameters into the scope of the function
body before the function itself has been added to the surrounding
scope. Fixes <rdar://problem/6097326>.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@62849 91177308-0d34-0410-b5e6-96231b3b80d8