cc is never a cross compiler in Nixpkgs. That cc probably comes from pkgsBuildBuild and exists so that builds can compile build tools that they can then use later in the build.

Yes, anything that hardcodes cc (or worse gcc) needs to be patched to support cross.

I ran into an issue while adding RISC-V runner support to nixpkgs-review-gha: https://github.com/Defelo/nixpkgs-review-gha/pull/126#issuecomment-4346267863

error: Cannot build '/nix/store/c9gf76p92n6n4933ilifdxi2npsz6ji0-expand-response-params.drv'.
       Reason: builder failed with exit code 139.
       Output paths:
         /nix/store/pg11yjn6k2p8ciadj750vrq3nndkzlzf-expand-response-params
       Last 7 log lines:
       > Running phase: unpackPhase
       > Running phase: patchPhase
       > Running phase: updateAutotoolsGnuConfigScriptsPhase
       > Running phase: configurePhase
       > no configure script, doing nothing
       > Running phase: buildPhase
       > /nix/store/hf467shdmb2grak3wsw0nb1x8qnn0vw1-bootstrap-stage1-stdenv-linux/setup: line 1769:    30 Segmentation fault         NIX_CC_USE_RESPONSE_FILE=0 "$CC" -std=c99 -O3 -o "expand-response-params" expand-response-params.c

Is this just an incompatibility with the C910 cores in the EM-RV1 boards?

I looked into it, and we currently pass --enable-default-pie so code compiled by gcc comes out PIE. But we are missing --enable-host-pie which changes how gcc itself is linked.

https://github.com/NixOS/nixpkgs/pull/514892