Fix Docker macOS timestamp issues and improve build reproducibility

- Add rsync-based source sync for Docker builds to fix macOS VirtioFS
  timestamp inconsistencies that caused autoconf sanity checks to fail
- Add config.sub wrapper (SHELL/CONFIG_SHELL) to support emscripten/wasm32
  targets without modifying submodule files
- Fix protobuf build to use native gcc/g++ for protoc instead of Emscripten
- Add python PATH fix for macOS (Homebrew's python3 symlink) in wxWidgets build

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

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

scripts/common/env.sh

@@ -11,6 +11,12 @@ export PROJECT_ROOT="$_KICAD_WASM_PROJECT_ROOT"
 export SCRIPTS_DIR="$_KICAD_WASM_SCRIPTS_DIR"
 export COMMON_DIR="$_KICAD_WASM_COMMON_DIR"
 
+# Use our config.sub wrapper for autoconf projects (emconfigure)
+# This intercepts config.sub calls to use our version with emscripten/wasm32 support
+# CONFIG_SHELL is critical: nested configures do SHELL=${CONFIG_SHELL-/bin/sh}
+export SHELL="$SCRIPTS_DIR/config/config-sub-wrapper.sh"
+export CONFIG_SHELL="$SCRIPTS_DIR/config/config-sub-wrapper.sh"
+
 # Build output directories (inside the project)
 export BUILD_ROOT="$PROJECT_ROOT/build-wasm"
 export DEPS_ROOT="$BUILD_ROOT/deps"