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