[dune] [configure] Fix `gramlib` path for hardcoded includes.
[dune] [configure] Fix `gramlib` path for hardcoded includes.

The regular make build uses a non-standard header path for their files
[as a way to workaround the ugliness of the non-hygienic build]

This breaks in Dune as it uses the regular object file pack, so
`coq_makefile` won't find it. We cherry pick a change from #8729 which
fixes the updated version of bug #9735 , even tho `coq_makefile`
should stop relying on hardcoded paths and use findlib instead.

Closes #9735

SkySkimmer/coq,coq/coq,Zimmi48/coq,gares/coq,coq/coq,Zimmi48/coq,gares/coq,ppedrot/coq,coq/coq,silene/coq,SkySkimmer/coq,silene/coq,Zimmi48/coq,ejgallego/coq,gares/coq,gares/coq,ppedrot/coq,silene/coq,JasonGross/coq,Matafou/coq,Zimmi48/coq,SkySkimmer/coq,Matafou/coq,ppedrot/coq,JasonGross/coq,ejgallego/coq,coq/coq,Matafou/coq,SkySkimmer/coq,JasonGross/coq,ppedrot/coq,gares/coq,JasonGross/coq,ppedrot/coq,ejgallego/coq,ejgallego/coq