[Bug d/94455] no [] operator overload for type

[ibuclaw at gdcproject dot org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94455

--- Comment #1 from Iain Buclaw <ibuclaw at gdcproject dot org> ---
Not compiler, but a missing library feature that was introduced in a more
recent version than what is bundled with gdc.

It could be backported for convenience, but if it can wait until after gcc-10,
then I hope to this time round sync with all master branches in upstream dlang,
and this pr will resolve itself with no further action.

That is assuming there's nothing blocking on introducing the necessary makefile
changes to support a self-hosted D front-end.