meson: treat -Wattributes as error

Trie relies on __attribute__(cleanup) and if its missing, it could
lead to memory leaks such as:

https://sonarcloud.io/project/issues?id=dns-oarc%3Adnsjit&issues=AXDyskhlrWLe1VCMvmVe&open=AXDyskhlrWLe1VCMvmVe
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