Add missing declarations of libzim.

The dependencies of libzim were missing.
If we run a single run to compile everything everything run correctly
as zlib and lzma will be installed because of kiwix-lib (and other)
dependencies.

dependencies.py

@@ -232,6 +232,7 @@ class Icu_cross_compile(Icu):
 
 class Libzim(Dependency):
     name = "libzim"
+    dependencies = ['zlib', 'lzma']
 
     class Source(GitClone):
         git_remote = "https://github.com/openzim/libzim.git"