Fix build issue of unittest.

Fix build issue of unittest.

When notification service unittest build with '-Wl, --as-needed' LDFLAGS,
some build machine building fail.(this flag is default option.)
The default of passing --as-needed can be undone by passing --no-as-needed to the linker.
So, 'Wl, --no-as-needed' flag is added in notification unittest SConscript.

Change-Id: Ifb56d0af433b58fc3bcbbd8938c9c318a21035c4
Signed-off-by: KIM JungYong <jyong2.kim@samsung.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/10127
Tested-by: jenkins-iotivity <jenkins-iotivity@opendaylight.org>
Reviewed-by: Madan Lanka <lanka.madan@samsung.com>