MHD_UNREACHABLE_: various fixes

src/mhd2/mhd_assert.h

@@ -82,7 +82,7 @@
 #  ifdef MHD_UNREACHABLE_
 #    undef MHD_UNREACHABLE_
 #  endif
-#  define MHD_UNREACHABLE_ ((void) 0)
+#  define MHD_UNREACHABLE_ (mhd_assert (0 && "Should not be reachable"))
 #endif
 
 #endif /* ! MHD_ASSERT_H */