rPackages.RcppArmadillo: fix darwin

[cideM]

Motivation for this change

Without this I get

/nix/store/47vpv5i10dwfg1cf5wca1k40f982g5fm-clang-wrapper-7.1.0/bin/c++ -std=gnu++11 -dynamiclib -Wl,-headerpad_max_install_names -undefined dynamic_lookup -single_module -multiply_defined suppress -L/nix/store/k20dhvmbiabz6v91qk324n9b8hpqjg1m-R-4.0.4/lib/R/lib -L/nix/store/3ndhndpas5zaxpa63gldf2xgcd2skd3y-libc++-7.1.0/lib -o RcppArmadillo.so RcppArmadillo.o RcppExports.o fastLm.o -L/nix/store/k20dhvmbiabz6v91qk324n9b8hpqjg1m-R-4.0.4/lib/R/lib -lRlapack -L/nix/store/k20dhvmbiabz6v91qk324n9b8hpqjg1m-R-4.0.4/lib/R/lib -lRblas -L/nix/store/jgq6753lj37wz7rxh03h8w7s2x7m9f0r-gfortran-9.3.0-lib/lib -L/nix/store/lsbcpdqhhnvxc1xmvyryihfv0wyf4mqi-gfortran-wrapper-9.3.0/bin -L/nix/store/pgs2br6vpd9y0cnq51pxpgxxs6y2x4l9-gfortran-9.3.0/lib/gcc/x86_64-apple-darwin/9.3.0 -L/nix/store/pgs2br6vpd9y0cnq51pxpgxxs6y2x4l9-gfortran-9.3.0/lib -lintl -liconv -lgfortran -lquadmath -lm -L/nix/store/k20dhvmbiabz6v91qk324n9b8hpqjg1m-R-4.0.4/lib/R/lib -lR -lintl -Wl,-framework -Wl,CoreFoundation
/nix/store/47vpv5i10dwfg1cf5wca1k40f982g5fm-clang-wrapper-7.1.0/bin/c++ -std=gnu++11 -dynamiclib -Wl,-headerpad_max_install_names -undefined dynamic_lookup -single_module -multiply_defined suppress -L/nix/store/k20dhvmbiabz6v91qk324n9b8hpqjg1m-R-4.0.4/lib/R/lib -L/nix/store/3ndhndpas5zaxpa63gldf2xgcd2skd3y-libc++-7.1.0/lib -o RcppArmadillo.so RcppArmadillo.o RcppExports.o fastLm.o -L/nix/store/k20dhvmbiabz6v91qk324n9b8hpqjg1m-R-4.0.4/lib/R/lib -lRlapack -L/nix/store/k20dhvmbiabz6v91qk324n9b8hpqjg1m-R-4.0.4/lib/R/lib -lRblas -L/nix/store/jgq6753lj37wz7rxh03h8w7s2x7m9f0r-gfortran-9.3.0-lib/lib -L/nix/store/lsbcpdqhhnvxc1xmvyryihfv0wyf4mqi-gfortran-wrapper-9.3.0/bin -L/nix/store/pgs2br6vpd9y0cnq51pxpgxxs6y2x4l9-gfortran-9.3.0/lib/gcc/x86_64-apple-darwin/9.3.0 -L/nix/store/pgs2br6vpd9y0cnq51pxpgxxs6y2x4l9-gfortran-9.3.0/lib -lintl -liconv -lgfortran -lquadmath -lm -L/nix/store/k20dhvmbiabz6v91qk324n9b8hpqjg1m-R-4.0.4/lib/R/lib -lR -lintl -Wl,-framework -Wl,CoreFoundation
ld: library not found for -liconv
ld: library not found for -liconv
clang-7: error: linker command failed with exit code 1 (use -v to see invocation)
clang-7: error: linker command failed with exit code 1 (use -v to see invocation)
make: *** [/nix/store/k20dhvmbiabz6v91qk324n9b8hpqjg1m-R-4.0.4/lib/R/share/make/shlib.mk:10: RcppArmadillo.so] Error 1
make: *** [/nix/store/k20dhvmbiabz6v91qk324n9b8hpqjg1m-R-4.0.4/lib/R/share/make/shlib.mk:10: RcppArmadillo.so] Error 1

on Darwin. I am a complete R beginner and as such took some inspiration from existing overrides.

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS linux)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Determined the impact on package closure size (by running nix path-info -S before and after)
• Ensured that relevant documentation is up to date
• Fits CONTRIBUTING.md.

[cideM]

Result of nixpkgs-review pr 123380 run on x86_64-darwin 1

[cideM]

Hm well calling nixpkgs-review didn't do much here, but $ nix-build -A rPackages.RcppArmadillo . can build the package from my branch