mkbundle commands for cross compilation. (#2970)

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