Fix wxrc build error by skipping native utilities

Add --without-subdirs flag to wxWidgets configure to prevent building
utils/, samples/, and demos/ directories. These contain native
applications like wxrc that shouldn't be cross-compiled to WASM.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

scripts/build-wxuniversal-wasm.sh

@@ -73,6 +73,7 @@ export CXXFLAGS="-DZ_HAVE_UNISTD_H=1 -I$PCRE2_INCLUDE"
 
 emconfigure "$WX_SOURCE/configure" \
     --host=emscripten \
+    --without-subdirs \
     --enable-universal \
     --disable-shared \
     --with-opengl \