Mostly picking the same paths as FreeBSD.
We need a little special handling for crt files, as netbsd uses its
own (and not GCC's) for those, with slightly different names.
* zig fmt
* std.mem.join takes a slice of slices instead of var args
* std.mem.join takes a separator slice rather than byte,
and always inserts it. Previously it would not insert the separator
if there already was one, violating the documented behavior.
* std.mem.join calculates exactly the correct amount to allocate
and has no call to allocator.shrink()
* bring back joinWindows and joinPosix and the corresponding tests.
it is intended to be able to call these functions from any OS.
* rename std.os.path.resolveSlice to resolve (now resolve takes
a slice of slices instead of var args)
