os2: improve absolute/full path handling for posix

core/os/os2/file_posix_darwin.odin

@@ -0,0 +1,18 @@
+//+private
+package os2
+
+import "base:runtime"
+
+import "core:sys/posix"
+
+_posix_absolute_path :: proc(fd: posix.FD, name: string, allocator: runtime.Allocator) -> (path: cstring, err: Error) {
+	F_GETPATH :: 50
+
+	buf: [posix.PATH_MAX]byte
+	if posix.fcntl(fd, posix.FCNTL_Cmd(F_GETPATH), &buf) != 0 {
+		err = _get_platform_error()
+		return
+	}
+
+	return clone_to_cstring(string(cstring(&buf[0])), allocator)
+}