Bring back useful comment

In b7b346c3e5 this conditional was simplified to just
`while( false)` rather than the current one. Then in 3a33315ff8, that
change was reverted. I found it hard to understand this
complicated conditional, but after some digging in history I found this
comment which used to be here. It was removed in b7b346c3e5, but not
restored together with the revert in 3a33315ff8. Let's revive it.

src/catch2/internal/catch_test_macro_impl.hpp

@@ -57,7 +57,8 @@
             CATCH_INTERNAL_STOP_WARNINGS_SUPPRESSION \
         } INTERNAL_CATCH_CATCH( catchAssertionHandler ) \
         INTERNAL_CATCH_REACT( catchAssertionHandler ) \
-    } while( (void)0, (false) && static_cast<const bool&>( !!(__VA_ARGS__) ) )
+    } while( (void)0, (false) && static_cast<const bool&>( !!(__VA_ARGS__) ) ) // the expression here is never evaluated at runtime but it forces the compiler to give it a look
+    // The double negation silences MSVC's C4800 warning, the static_cast forces short-circuit evaluation if the type has overloaded &&.
 
 ///////////////////////////////////////////////////////////////////////////////
 #define INTERNAL_CATCH_IF( macroName, resultDisposition, ... ) \