os2: improve absolute/full path handling for posix

core/os/os2/file_posix_other.odin

@@ -0,0 +1,21 @@
+//+private
+//+build openbsd
+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) {
+	TEMP_ALLOCATOR_GUARD(ignore=is_temp(allocator))
+	cname := temp_cstring(name)
+
+	buf: [posix.PATH_MAX]byte
+	path = posix.realpath(cname, raw_data(buf[:]))
+	if path == nil {
+		err = _get_platform_error()
+		return
+	}
+
+	return clone_to_cstring(string(path), allocator)
+}