cerbero/filesprovider: Be stricter when finding plugin DLLs
cerbero/filesprovider: Be stricter when finding plugin DLLs

Do not look for a `libfoo.dll` plugin when the recipe has been built
with MSVC. This avoids incorrect packaging when the prefix is dirty
due to user error.

fluendo/cerbero,fluendo/cerbero,fluendo/cerbero,fluendo/cerbero,fluendo/cerbero