build: Improve target message in build_common

build: Improve target message in build_common

Improve the text of host/target unsup message in build_common

No operational changes

Change-Id: I6a8b95fac210a8f80132bebab148a67dfa76d51d
Signed-off-by: Mats Wichmann <mats@linux.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/19637
Tested-by: jenkins-iotivity <jenkins@iotivity.org>
Reviewed-by: Phil Coval <philippe.coval@osg.samsung.com>
(cherry picked from commit 570d343aa00bb5b503c7c6cea904eb52691a42e0)
Bug: https://jira.iotivity.org/browse/IOT-1745
Signed-off-by: Phil Coval <philippe.coval@osg.samsung.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/20579
Reviewed-by: Habib Virji <habib.virji@samsung.com>