Enable `clang-tidy`'s `clang-analyzer-unix.Malloc` check

[qdeslandes]

This check would have saved use from a bug fixed in #393. However, enabling it creates a lot of false positives, because clang-tidy don't acknowledge the cleanup attribute. There could be a way to solve this as per https://clang.llvm.org/docs/AttributeReference.html#analyzer-ownership-attrs.