Link samples using STC with imm32.lib

This completes the changes of f730da3c14 (Add imm32.lib to
wxStyledTextCtrl, 2020-05-10) that didn't take care of MSW makefiles,
that need to contain the new required library as well.

Closes #18788.

build/bakefiles/wxwin.py

@@ -51,6 +51,7 @@ EXTRALIBS = {
     'html' : '$(EXTRALIBS_HTML)',
     'adv' : '$(PLUGIN_ADV_EXTRALIBS)',
     'media' : '$(EXTRALIBS_MEDIA)',
+    'stc' : '$(EXTRALIBS_STC)',
     'webview' : '$(EXTRALIBS_WEBVIEW)',
 }