Make GcovImporter::setRunner() return old value

This way runner can be restored.

Author: xaizek

src/GcovImporter.cpp

@@ -138,10 +138,12 @@ GcovInfo::GcovInfo()
     }
 }
 
-void
+std::function<GcovImporter::runner_f>
 GcovImporter::setRunner(std::function<runner_f> runner)
 {
+    std::function<runner_f> previous = std::move(getRunner());
     getRunner() = std::move(runner);
+    return previous;
 }
 
 GcovImporter::GcovImporter(const std::string &root,

src/GcovImporter.hpp

@@ -85,8 +85,10 @@ class GcovImporter
      * There is no runner by default.
      *
      * @param runner New runner.
+     *
+     * @returns Previous runner.
      */
-    static void setRunner(std::function<runner_f> runner);
+    static std::function<runner_f> setRunner(std::function<runner_f> runner);
 
 public:
     /**