[IOT-1996] Make resource/csdk/connectivity W4 compliant.

[IOT-1996] Make resource/csdk/connectivity W4 compliant.

These changes include the following:
- Fix W4 warnings under resource/csdk/connectivity.
- Fix W4 warnings under resource/csdk/connectivity/test.
- Enable /W4 /WX on resource/csdk/connectivity.
- Enable /W4 /WX on resource/csdk/connectivity/test.
- Update build_common/Windows/SConscript.

Change-Id: I98d93f4df6fc938f004ef2f6844ba120bb5e788a
Signed-off-by: Alex Kelley <alexke@microsoft.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/18535
Tested-by: jenkins-iotivity <jenkins@iotivity.org>
Reviewed-by: Dan Mihai <Daniel.Mihai@microsoft.com>
Reviewed-by: Mike Fenelon <mike.fenelon@microsoft.com>
(cherry picked from commit 7a811cc5b6ba90a99ada4a86da1632367a52304c)
Reviewed-on: https://gerrit.iotivity.org/gerrit/18749
Reviewed-by: Dave Thaler <dthaler@microsoft.com>