Merge pull request #343 from hzeller/20220531-purge-serializer

The UHDM Serializer leaks memory if not Purge()-ed, so call it after …
diff --git a/systemverilog-plugin/uhdmastfrontend.cc b/systemverilog-plugin/uhdmastfrontend.cc
index 660b4c2..4874ee8 100644
--- a/systemverilog-plugin/uhdmastfrontend.cc
+++ b/systemverilog-plugin/uhdmastfrontend.cc
@@ -57,6 +57,8 @@
         }
         for (auto design : restoredDesigns)
             vpi_release_handle(design);
+
+        serializer.Purge();
         return current_ast;
     }
     void call_log_header(RTLIL::Design *design) override { log_header(design, "Executing UHDM frontend.\n"); }