* fix sb-posix time structs to match headers on darwin
* comment out mtime sb-posix test as this isn't working ATM
* add UD2A trap stuff to x86-64 and corresponding word-imm support
* remove bogus extern-alien-name in boxed_region fixups
* add compiler parameters for Darwin
* add x86-64 darwin config file
* some type safety fixes (proper types) in darwin-dlshim.c
* use setpgid on Darwin
* add signal context support x86-64/darwin
* report trap instead of si_code for trap_Error/trap_Cerror
* unsigned -> unsigned long in purify.c
* add mach exception handler support for x86-64/darwin
* x86-64 assembly hacks to make darwin's assembler happy
* update x86-64-bsd-os.c to suppot darwin and mach exceptions
* add x86-64-darwin-os.c/h
* update LDSO stubs for x86-64 darwin