mavsdk_server: fix dl-lib linking #3519

Job	Run time
alpine 3.11.6 (musl)	19m 21s
coverage (ubuntu-20.04)	3m 53s
Ubuntu/Debian packaging (Ubuntu 20.04)	5m 49s
ubuntu-20.04 (package, non-mavsdk_server)	4m 22s
android-arm	11m 2s
android-arm64	22m 44s
linux-armv6	4m 20s
manylinux2010-x64	23m 7s
android-x86	11m 23s
linux-armv6-musl	18m 35s
linux-armv7	4m 19s
android-x86_64	19m 54s
linux-armv7l-musl	18m 7s
linux-arm64	4m 19s
linux-arm64-musl	19m 18s
ios	16m 2s
macOS	26m 10s
ios_simulator	15m 48s
fedora-34 (package, non-mavsdk_server)	4m 7s
macOS-framework	23m 25s
ubuntu-20.04 (check style and docs)	3m 31s
fedora-35 (package, non-mavsdk_server)	3m 48s
ubuntu-20.04 (mavsdk, hunter)	3m 1s
ubuntu-20.04 (non-mavsdk_server, non-superbuild)	3m 11s
ubuntu-20.04 (mavsdk_server, superbuild)	16m 37s
ubuntu-20.04 (proto check)	15m 53s
Windows	36m 22s
iOS XCFramework	0s
	5h 58m 28s

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