rustc: disable parallel building

http://hydra.nixos.org/build/33119905/nixlog/1/raw

Changed files
+1 -1
pkgs
development
compilers
rustc
+1 -1
pkgs/development/compilers/rustc/generic.nix
···
buildInputs = [ ncurses ]
++ optional (!forceBundledLLVM) llvmShared;
-
enableParallelBuilding = true;
+
enableParallelBuilding = false; # missing files during linking, occasionally
outputs = [ "out" "doc" ];