build: Windows: Work around coap.h race

build: Windows: Work around coap.h race

Build coap.h before everything else, to work around an apparent
multi-threaded build race condition.

Bug: https://jira.iotivity.org/browse/IOT-2376
Change-Id: Ic112cfea42dfa1ac12735b4af882dc45a74c853d
Signed-off-by: Dan Mihai <Daniel.Mihai@microsoft.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/20891
Reviewed-by: Phil Coval <philippe.coval@osg.samsung.com>
Reviewed-by: Ibrahim Esmat <iesmat@microsoft.com>
Tested-by: jenkins-iotivity <jenkins@iotivity.org>
Reviewed-by: Omar Maabreh <omarm@microsoft.com>