And add test cases to ensure that this works
- 110 verifies that glcpp rejects #elif<digits> which glcpp
previously accepted.
- 111 verifies that glcpp accepts #if followed immediately by
(, +, -, !, or ~.
- 112 does the same as 111 but for #elif.
See 17f9beb6 for #if change.
Reviewed-by: Carl Worth <cworth@cworth.org>
