Treat -mios-simulator-version-min option as an alias for -mios-version-min.

We can safely rely on the architecture to distinguish iOS device builds from
iOS simulator builds. We already have code to do that, in fact. This simplifies
some of the error checking for the option handling.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@219545 91177308-0d34-0410-b5e6-96231b3b80d8