AWT support for SE-Embedded integration

This CR integrates support for SE-Embedded into the AWT. The main changes are:

- forward-port from JDK6 the replacement of hard-wired X11 paths to use OPENWIN_HOME-based paths
- cross-compilation support
- Support for BUILD_HEADLESS_ONLY, which is a specialized build for environments where there are no X11 libraries available at build-time. X11 headers are still needed due to various dependencies in the native code
- Customize the tray-icon timeout for slow devices
- Add new HToolkit for headless environments without any xawt support (used for SE-Embedded reduced-headless builds)
- Update logic for default toolkit selection on Solaris/Linux (AWT team request)
- SE-Embedded specific customizations (conditional on defining JAVASE_EMBEDDED in the build variables)
- New AWT event polling algorithm with changed defaults for SE-Embedded (SE behaviour remains the same)