Test go to definition of control variable of cilk_for loop

[VoxSciurorum]

I was unable to make this test fail by backing out recent changes to clangd. The test program is

void f() {
  _Cilk_for(int ii = 99; ii < 999; ii += 1) { int jj = ii;};
}

and the definition to be looked up is ii.

[neboat]

Sorry, I made a mistake before when we talked about this. It looks like that go-to-definition is actually one of the few that does work without the recent clangd changes.

Here are some examples of other failures without those clangd changes:

In contrast, these go-to-definitions work after the clangd changes:

[VoxSciurorum]

I updated the test to fail on dev/16.x and pass on dev/18.x.