Forgive me if this is dumb - I am fairly new to nixos. But I'm not sure how I got my setup messed up:

~ $ gcc -xc - <<< 'int main(){}'
/nix/store/hrkc2sf2883l16d5yq3zg0y339kfw4xv-binutils-2.31.1/bin/ld: symbol lookup error: /nix/store/hrkc2sf2883l16d5yq3zg0y339kfw4xv-binutils-2.31.1/bin/ld: undefined symbol: xmemdup
collect2: error: ld returned 127 exit status