Clang has attribute ext_vector_type which is like vector_size but it accepts number of lanes. This is used by some vector code and while it can be replaced by multiplication by sizeof (elt_type) it may be good idea to add it.
It turns out that ext_vector_type attribute is not only about declaring vector variable but also affects semantics. Brief documentation is in https://clang.llvm.org/docs/LanguageExtensions.html#vectors-and-extended-vectors and see also discussion in http://hubicka.blogspot.com/2018/12/even-more-fun-with-building-and.html I can confirm that Skia code is somewhat more compact/ergonomic with the extension though i still do not fully understand the design.