swift234

simd module: Only provide '&+', '&-', and '&*' variants of arithmetic operators.

Checked arithmetic is probably not what you want from the vector unit, but we still want code to be explicit about the fact that it's using wrapping semantics instead of trapping or UB semantics. Provide the wrapping variations of the operators, and leave behind unavailable definitions to direct users to the wrapping operations if they try to use the standard ones.

Swift SVN r30008