ARM: mark matching ARM intrinsics as MSBuiltin

A number of the ARM intrinsics are aliased with alternative names in MSVC
compatibility mode.  This change indicates those intrinsics to permit tablegen
to construct an appropriate list of MSBuiltins.  With the corresponding change
in clang, these intrinsics can then be mapped from the frontend.

The tests to validate the intrinsics are aliased correctly will be added with
the corresponding clang change.