fix setting of INDEX and POINTER data-items

[GitMensch]

needing SET, not MOVE

note: GnuCOBOL and ACUCOBOL-GT don't enforce this ISO rule, but this would fail to compile at least on IBM, so fixing it is

[meyfa]

Yes, this should be done. Thanks for raising the issue!

There are many more instances of MOVE in place of SET. Is there an option to let GnuCOBOL enforce this rule specifically (besides going straight to full IBM compatibility)? I've had a look at the GC guide but couldn't find any option.

This would be helpful to prevent regressions, and also to find every occurrence initially.

[GitMensch]

No, it is most likely reasonable to try compiling with a different compiler. gcobol may be possible after FOSDEM (COBOLworx wants to work on / push some necessary changes and can then likely be both installed per .deb and bring a "cobc driver" gcobc, where make COBC=gcobc GCVERSION=32 should do the trick.
I am likely to give that a go in 2-3 weeks and could work on this PR then (until then gnucobol will still compile that).