rstan without v8 dependency

[barracuda156]

Is there a current version without a dependency on v8? @andrjohns had a fork earlier: https://discourse.mc-stan.org/t/override-dependency-on-v8-or-make-v8-build-on-powerpc-mac-r-4-1-2/25432/5 (which still failed to build the last time I tried).

I want to fix rstan for MacOS PPC. The major issue, as of now, is a lack of Darwin PPC support in v8. There is some version of v8 for PPC, perhaps dated, but it is for AIX – rewriting it for Darwin may be feasible, but far from trivial: https://github.com/ibmruntimes/v8ppc

P. S. For the context, we have the latest cmake, gcc11 with gfortran and the latest R working on MacOS PPC. Many R packages build, some fail. There is no qt5 for PPC, so RStudio does not build, but I have fixed a reasonable recent version of R GUI app.