Fix Wunused-variable warning for MinGW

Closes #2132

src/catch2/internal/catch_run_context.cpp

@@ -500,6 +500,11 @@ namespace Catch {
         // before running the tests themselves, or the binary can crash
         // without failed test being reported.
         FatalConditionHandlerGuard _(&m_fatalConditionhandler);
+        // We keep having issue where some compilers warn about an unused
+        // variable, even though the type has non-trivial constructor and
+        // destructor. This is annoying and ugly, but it makes them stfu.
+        (void)_;
+
         m_activeTestCase->invoke();
     }