win: Include stddef.h for offsetof()

A future libc++ revision will stop providing this include transitively.

Bug: 376278210
Change-Id: I79460933ed915bc601278a6d75f2c2ced1130440
Reviewed-on: https://chromium-review.googlesource.com/c/crashpad/crashpad/+/6049220
Commit-Queue: Nico Weber <thakis@chromium.org>
Reviewed-by: Mark Mentovai <mark@chromium.org>

handler/win/wer/crashpad_wer.cc

diff --git a/handler/win/wer/crashpad_wer.cc b/handler/win/wer/crashpad_wer.cc
index 1394e20..1973e7f 100644
--- a/handler/win/wer/crashpad_wer.cc
+++ b/handler/win/wer/crashpad_wer.cc
@@ -20,6 +20,7 @@
 #include "util/misc/address_types.h"
 #include "util/win/registration_protocol_win_structs.h"
 
+#include <stddef.h>
 #include <Windows.h>
 #include <werapi.h>