libroot: add timespec_get to build

* Added in hrev55773

Change-Id: Ib57b53c76641e87c5ac0c0cde2407a7bfe45ce41
Reviewed-on: https://review.haiku-os.org/c/haiku/+/4935
Reviewed-by: Jessica Hamilton <jessica.l.hamilton@gmail.com>
Tested-by: Commit checker robot <no-reply+buildbot@haiku-os.org>

src/system/libroot/posix/time/Jamfile

@@ -33,6 +33,7 @@ for architectureObject in [ MultiArchSubDirSetup ] {
 			timelocal.cpp
 			time.c
 			timer_support.cpp
+			timespec_get.cpp
 			wcsftime.c
 			;
 	}