CRT in generated parser

Hi folks, I'm working on a tool that uses flex/bison and runs in rather
scarce environment thus needs C runtime substitution.

Tool employs reentrant scanner/parser. As far as I can see bison 3.0.4
(default on Ubuntu 18.04) and latest git version both

generates yypstate_new/yypstate_delete using straightforward calls to
malloc() and free(). Is it possible to override this?

I see YYMALLOC/YYFREE used in other parts of generated parser's code,
perhaps, they could be used in yypstate* routines as well?

Is there any best known method for substituting runtime in generated parser
code? (besides, SED-like search-replace).

WBR,

--Kovalex