Fix link error for test_radixtree module on Windows

Add back "link_with" directive, similar to the one removed by 1f1d73a8b,
but only for Windows, but use the "_shlib" variation.

Diagnosis by Masahiko Sawada, proposed fix adjusted and tested by me

Per buildfarm members drongo and fairywren

Discussion: https://postgr.es/m/CAD21AoAMm1mQd%3Dw4PrfrKK%3DOMP8j8%3D7ntJRPF8%2B%3D10iUuvwiCA%40mail.gmail.com

src/test/modules/test_radixtree/meson.build

@@ -12,6 +12,7 @@ endif
 
 test_radixtree = shared_module('test_radixtree',
   test_radixtree_sources,
+  link_with: host_system == 'windows' ? pgport_shlib : [],
   kwargs: pg_test_mod_args,
 )
 test_install_libs += test_radixtree