remove artiq dependency on rustc

artiq-fast/pkgs/libartiq-support.nix

@@ -2,12 +2,15 @@
 stdenv.mkDerivation rec {
   name = "libartiq-support-${version}";
   version = import ./artiq-version.nix { inherit stdenv fetchgit git; };
+
   src = import ./artiq-src.nix { inherit fetchgit; };
+
+  buildInputs = [ rustc ];
   phases = [ "buildPhase" ];
   # keep in sync with artiq/test/lit/lit.cfg or remove build from the latter once we don't use buildbot/conda anymore
   buildPhase =
   ''
   mkdir $out
-  ${rustc}/bin/rustc ${src}/artiq/test/libartiq_support/lib.rs --out-dir $out -Cpanic=unwind -g
+  rustc ${src}/artiq/test/libartiq_support/lib.rs --out-dir $out -Cpanic=unwind -g
   '';
 }