library-cmp: Handle filters for the fully-qualified symbols name

If a filter pattern has an '@' in it, it's safe to assume that it is
expected to be compared against the `symbol@version` fully-qualified
name.
Instead if there isn't an '@', like before, we just compare it against
only the symbol.

Signed-off-by: Ludovico de Nittis <ludovico.denittis@collabora.com>
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