SAN FRANCISCO (Reuters) – Microsoft Corp said on Wednesday it would give away its Windows operating system to makers of smartphones and small tablets as it seeks to grab a toehold in those fast-growing markets. Microsofts move, announced at its annual developers conference in San Francisco, is an attempt to broaden the user base of mobile versions of Windows, in the hope that more customers will end up using Microsofts cloud-based services such as Skype and Office. …