Refactor Gambit support

Refactor the build rule:
- Put files in $out/gambit instead of $out.
- Make the optimization setting easy to override.
- Make use of gccStdenv more explicit at this level.
- Support new-style runtime options for forcing UTF-8 I/O.
- Override the PACKAGE_VERSION and PACKAGE_STRING with git version.
- Note that the license is lgpl21, not lpgl2 (Note: also dual asl20).
- Try and fail to meaningfully add missing runtimeDeps.
- Build using NIX_BUILD_CORES.

pkgs/development/compilers/gambit/default.nix

@@ -1,10 +1,10 @@
-{ stdenv, callPackage, fetchurl }:
+{ callPackage, fetchurl }:
 
-callPackage ./build.nix {
+callPackage ./build.nix rec {
   version = "4.9.3";
+  git-version = version;
   src = fetchurl {
     url = "http://www.iro.umontreal.ca/~gambit/download/gambit/v4.9/source/gambit-v4_9_3.tgz";
     sha256 = "1p6172vhcrlpjgia6hsks1w4fl8rdyjf9xjh14wxfkv7dnx8a5hk";
   };
-  inherit stdenv;
 }