compiler_rt: addXf3: add coercion to `@clz`
compiler_rt: addXf3: add coercion to `@clz`

We're going to remove the first parameter from this function in the
future. Stage2 already ignores the first parameter. So we put an `@as`
in here to make it work for both.

andrewrk/zig,andrewrk/zig