IOT-1961: Fixing Windows c_common test build environment.

IOT-1961: Fixing Windows c_common test build environment.

One test was missing the /W4 and /WX compiler options, because
it was using a default test environment variable.

Change-Id: I095d612e6778576384a4b78abf3a97b958e5f5ee
Signed-off-by: Pawel Winogrodzki <pawelwi@microsoft.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/18175
Tested-by: jenkins-iotivity <jenkins@iotivity.org>
Reviewed-by: Alex Kelley <alexke@microsoft.com>
Reviewed-by: Soemin Tjong <stjong@microsoft.com>
Reviewed-by: Phil Coval <philippe.coval@osg.samsung.com>
Reviewed-by: Dave Thaler <dthaler@microsoft.com>