Make liblttng-ust_sys-sdt.h pass when lttng is not installed #628

Job	Run time
Verify tests pass (docker.io/library/alpine:latest, 6.0)	7m 46s
Verify tests pass (docker.io/library/alpine:latest, 8.0)	8m 4s
Verify tests pass (docker.io/library/alpine:edge, 6.0)	7m 6s
Verify tests pass (docker.io/library/alpine:edge, 8.0)	8m 5s
Verify tests pass (quay.io/centos/centos:stream9, 6.0)	8m 1s
Verify tests pass (quay.io/centos/centos:stream9, 8.0)	8m 9s
Verify tests pass (registry.fedoraproject.org/fedora:39, 6.0)	8m 15s
Verify tests pass (registry.fedoraproject.org/fedora:39, 8.0)	9m 13s
Verify tests pass (registry.fedoraproject.org/fedora:40, 6.0)	7m 45s
Verify tests pass (registry.fedoraproject.org/fedora:40, 8.0)	8m 55s
Verify tests pass (registry.fedoraproject.org/fedora:rawhide, 8.0)	8m 20s
Verify tests pass (registry.access.redhat.com/ubi8, 6.0)	8m 21s
Verify tests pass (registry.access.redhat.com/ubi8, 8.0)	8m 29s
Verify tests pass (registry.access.redhat.com/ubi9, 6.0)	7m 18s
Verify tests pass (registry.access.redhat.com/ubi9, 8.0)	7m 59s
Verify tests pass (registry.fedoraproject.org/fedora:40, 9.0)	8m 37s
	2h 10m 23s

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