Missing run-export on libgcc-ng on linux

[h-vetinari]

As seen in conda-forge/staged-recipes#26081, where it was necessary to add {{ compiler("c") }} just to get its run-export on libgcc-ng.

If rust-compiled binaries end up needing libgcc_s.so.1, we should add the run-export here.

[isuruf]

We don't know what version of libgcc_s.so the rust compiler will use, so we don't know what the run_exports minimum version should be. Need some sort of transitive dependency run_exports.

[h-vetinari]

The SOVERSIONs of the libraries in libgcc-ng haven't changed since at least GCC 8, down to the patch level. They're not as sensitive to the runtime version as libstdcxx, so AFAICT we should be fine with libgcc-ng >= 11.4, i.e. the minimal GCC version we're still building.

It would IMO be an improvement over the current situation.