tests.buildRustCrate: add rcgen test

rcgen depends on ring, and therefore exercises support for static libraries

pkgs/build-support/rust/build-rust-crate/test/default.nix

@@ -548,6 +548,10 @@ let
       };
     };
     brotliCrates = (callPackage ./brotli-crates.nix {});
+    rcgenCrates = callPackage ./rcgen-crates.nix {
+      # Suppress deprecation warning
+      buildRustCrate = null;
+    };
     tests = lib.mapAttrs (key: value: mkTest (value // lib.optionalAttrs (!value?crateName) { crateName = key; })) cases;
   in tests // rec {
 
@@ -645,6 +649,16 @@ let
     } ''
       test -e ${pkg}/bin/brotli-decompressor && touch $out
     '';
+
+    rcgenTest = let
+      pkg = rcgenCrates.rootCrate.build;
+    in runCommand "run-rcgen-test-cmd" {
+      nativeBuildInputs = [ pkg ];
+    } (if stdenv.hostPlatform == stdenv.buildPlatform then ''
+      ${pkg}/bin/rcgen && touch $out
+    '' else ''
+      test -x '${pkg}/bin/rcgen' && touch $out
+    '');
   };
   test = releaseTools.aggregate {
     name = "buildRustCrate-tests";