nix: native: Add relibc deps

Fixes relibc building:

warning: relibc@0.2.5:
/mnt/redox/prefix/x86_64-unknown-redox/gcc-freestanding-install/bin/ \
../libexec/gcc/x86_64-unknown-redox/13.2.0/cc1: error while loading \
shared libraries:  libmpc.so.3: cannot open shared object file: No \
such file or directory
error: failed to run custom build command for `relibc v0.2.5 \
(/mnt/redox/recipes/core/relibc/source)`

flake.nix

@@ -154,6 +154,9 @@
 
           buildInputs = with pkgs; [
             (pkgs.rust-bin.fromRustupToolchainFile ./rust-toolchain.toml)
+            gmp # relibc
+            mpfr # relibc
+            libmpc # relibc
             fuse # fuser
             libpng # netsurf
             fontconfig # orbutils