[1.10>master] [MERGE #5384 @sethbrenith] fix a warning about buffer bounds
[1.10>master] [MERGE #5384 @sethbrenith] fix a warning about buffer bounds

Merge pull request #5384 from sethbrenith:user/sethb/prefast

Tell the static analysis tool that UInt32Math::Add adds and guarantees no overflow.

Fixes OS:18017387

Microsoft/ChakraCore,Microsoft/ChakraCore,Microsoft/ChakraCore,Microsoft/ChakraCore,Microsoft/ChakraCore,Microsoft/ChakraCore