syscall: add DLLError.Unwrap function
Because we're expecting for future functions to be unavailable, we
should add an Unwrap() function to the DLLError struct, so that people
can test for this situation easily via:
if errors.Is(err, syscall.ERROR_PROC_NOT_FOUND) { ... }
DLLError already was wrapping the underlying Errno error, but never got
the Go 1.13 helper method.
Fixes golang/go#42584
Change-Id: I0f32a5146946b1b37a30897ba825a56faefc792c
Reviewed-on: https://go-review.googlesource.com/c/go/+/269761
Run-TryBot: Jason A. Donenfeld <Jason@zx2c4.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Alex Brainman <alex.brainman@gmail.com>
Trust: Alex Brainman <alex.brainman@gmail.com>
Trust: Jason A. Donenfeld <Jason@zx2c4.com>