scons: Disable spurious "array-bounds" warnings for protobuf cc files.

These files are generated and so, even if they're wrong, there isn't
anything we can do about it.

Change-Id: I933057a04f09dd1c22b525a102278bbdc5fbc22b
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/24924
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Gabe Black <gabeblack@google.com>
Tested-by: kokoro <noreply+kokoro@google.com>

src/SConscript

@@ -1027,7 +1027,8 @@ if env['HAVE_PROTOC'] and env['HAVE_PROTOBUF']:
                                Transform("PROTOC")))
 
         # Add the C++ source file
-        Source(proto.cc_file, tags=proto.tags)
+        Source(proto.cc_file, tags=proto.tags,
+                append={'CXXFLAGS': '-Wno-array-bounds'})
 elif ProtoBuf.all:
     error('Got protobuf to build, but lacks support!')