Refactor wimpy feature (#2507)

- Make it a common parameter in harness using either '-w', '--wimpy' or
'CL_WIMPY_MODE' environment variable.
- Remove all test specific wimpy variable.

---------

Co-authored-by: Kévin Petit <kpet@free.fr>

test_conformance/half/Test_vStoreHalf.cpp

@@ -16,6 +16,7 @@
 #include "harness/compat.h"
 #include "harness/kernelHelpers.h"
 #include "harness/testHarness.h"
+#include "harness/parseParameters.h"
 
 #include <string.h>