build: made environment access a separate feature

modules/dnn/perf/perf_main.cpp

@@ -1,16 +1,7 @@
 #include "perf_precomp.hpp"
 
-static const char* extraTestDataPath =
-#ifdef WINRT
-        NULL;
-#else
-        getenv("OPENCV_DNN_TEST_DATA_PATH");
-#endif
-
 #if defined(HAVE_HPX)
     #include <hpx/hpx_main.hpp>
 #endif
 
-CV_PERF_TEST_MAIN(dnn,
-    extraTestDataPath ? (void)cvtest::addDataSearchPath(extraTestDataPath) : (void)0
-)
+CV_PERF_TEST_MAIN(dnn, cvtest::addDataSearchEnv("OPENCV_DNN_TEST_DATA_PATH"))