Add the dont_skip attribute on dependency.

Instead of explicitly add the target associated to the toolchain
if we use `build_nodeps` option let add an attribute base ourself on it
to know if we need to add it or not.

This way, we may have other dependency we must not skip.

kiwixbuild/dependencies/base.py

@@ -23,6 +23,7 @@ class Dependency(metaclass=_MetaDependency):
     all_deps = {}
     force_build = False
     force_native_build = False
+    dont_skip = False
 
     @classmethod
     def version(cls):