Fix all GCC 10 warnings

Change-Id: Ibabab265e734a4a421a38ab586e7e11905fa5da1
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/64740
Reviewed-by: Austin Eng <enga@chromium.org>
Commit-Queue: Ben Clayton <bclayton@google.com>

generator/templates/webgpu_cpp.cpp

@@ -17,6 +17,11 @@
     #include "webgpu/webgpu_cpp.h"
 {% endif %}
 
+#ifdef __GNUC__
+// error: 'offsetof' within non-standard-layout type 'wgpu::XXX' is conditionally-supported
+#pragma GCC diagnostic ignored "-Winvalid-offsetof"
+#endif
+
 namespace wgpu {
     {% for type in by_category["enum"] %}
         {% set CppType = as_cppType(type.name) %}