build: include stubs in shared library

This is needed for external applications that link to shared libnode.
Fixes #27431

PR-URL: https://github.com/nodejs/node/pull/28897
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Rich Trott <rtrott@gmail.com>

node.gyp

@@ -686,6 +686,12 @@
       'msvs_disabled_warnings!': [4244],
 
       'conditions': [
+        [ 'node_shared=="true"', {
+          'sources': [
+            'src/node_snapshot_stub.cc',
+            'src/node_code_cache_stub.cc',
+          ]
+        }],
         [ 'node_shared=="true" and node_module_version!="" and OS!="win"', {
           'product_extension': '<(shlib_suffix)',
           'xcode_settings': {