[Bug fortran/96255] [F2018] Implement optional type spec for index in DO CONCURRENT

[jvdelisle at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96255

--- Comment #26 from Jerry DeLisle <jvdelisle at gcc dot gnu.org> ---
With the last minor fixer, we'll see if that removes any builder breakage. Then
remaining will be the error message in Comment #22