Add m68k to recognized CPUs (machinetype)
Add amigaos to recognized operating systems (osversion)
Add ability to override "config.guess" output w/ LDEARCH= to osversion
Add platform.h clauses to recognize AmigaOS 3 using gcc to cross-compile
Update osversion script to recognize x86_64 triples for Darwin as Darwin
Update machinetype script to return 386 for MacOS El Capitan (10.11), x86_64 for other versions
Add makefile-darwin.x86_64-x for compiling in 64-bit mode on later MacOS versions
modified: config.guess
modified: machinetype
new file: makefile-darwin.x86_64-x
modified: osversion
