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 <ba8e1833495515b49ded9e20cae80a8129155aa9@microsoft.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/20891
Reviewed-by: Phil Coval <ff46fec9739d31cce915aabcc3a7a2c00eee4d6c@osg.samsung.com>
Reviewed-by: Ibrahim Esmat <eccbe9b3ebe108c7d8ef87d35d7429eb0351868b@microsoft.com>
Tested-by: jenkins-iotivity <d95b56ce41a2e1ac4cecdd398defd7414407cc08@iotivity.org>
Reviewed-by: Omar Maabreh <3a8c539dd1468e5c297e7063158b75a45dd3bf69@microsoft.com>

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