mkbundle commands for cross compilation. (#2970)
* Start of packager for mkbundle
* [mkbundle] Add fingerprint and directory at end of package
* [mkbundle] Update embedding file format, add support for --options, support for --runtime, chmod +x
* [driver] Add a way to parse arbitrary command line options
* [mkbundle] Align the assemblies on a page boundary, do not release directory buffer
* Work-around odd compiler error by using memcpy
* Update makefile
* Fix the windows build
* [Windows] Export the new mono_parse_options_from API
* Implement the various cross-compiler target fetching commands
* Clean