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/gambit-support.nix

@@ -0,0 +1,33 @@
+{ pkgs, lib }:
+
+rec {
+  stable-params = {
+    defaultRuntimeOptions = "f8,-8,t8";
+    buildRuntimeOptions = "f8,-8,t8";
+    fix-stamp = git-version : "";
+  };
+
+  unstable-params = {
+    defaultRuntimeOptions = "iL,fL,-L,tL";
+    buildRuntimeOptions = "i8,f8,-8,t8";
+    fix-stamp = git-version : ''
+      substituteInPlace configure \
+        --replace "$(grep '^PACKAGE_VERSION=.*$' configure)" 'PACKAGE_VERSION="v${git-version}"' \
+        --replace "$(grep '^PACKAGE_STRING=.*$' configure)" 'PACKAGE_STRING="Gambit v${git-version}"' ;
+    '';
+  };
+
+  export-gambopt = params : "export GAMBOPT=${params.buildRuntimeOptions} ;";
+
+  gambit-bootstrap = import ./bootstrap.nix ( pkgs );
+
+  meta = {
+    description = "Optimizing Scheme to C compiler";
+    homepage    = "http://gambitscheme.org";
+    license     = lib.licenses.lgpl21; # dual, also asl20
+    # NB regarding platforms: continuously tested on Linux,
+    # tested on macOS once in a while, *should* work everywhere.
+    platforms   = lib.platforms.unix;
+    maintainers = with lib.maintainers; [ thoughtpolice raskin fare ];
+  };
+}