Handle void correctly in the argument list for a function. For:

  X = sizeof(int (void a));
  X = sizeof(int (int, void));
  X = sizeof(int (void, ...));

We now emit:

t.c:6:24: error: void argument may not have a name
  X = sizeof(int (void a));
                       ^
t.c:7:24: error: 'void' must be the first and only parameter if specified
  X = sizeof(int (int, void));
                       ^
t.c:8:19: error: 'void' must be the first and only parameter if specified
  X = sizeof(int (void, ...));
                  ^


And we pretty print this correctly (even though void isn't stored in the
arg list of the function type):
  X = sizeof(int (void));


However, this approach will have to change to handle typedefs of void.

llvm-svn: 39235