In dynamic dispatching, Highway pushes function attributes such as "+sve" onto
functions to compile them for specific targets.

Clang and GCC rely on the "-msve-vector-bits=128" option to specialize
functions for 128 bit SVE vectors, but this flag applies specialized attributes
at a compilation unit granularity, and therefore cannot be pushed to individual
functions. The absence of this flag means useful information about the vector
length of SVE2_128 functions can be lost to intermediate compiler languages
such as LLVM IR.

Using Lanes(d) for SVE2_128 masked intrinsics gives compilers the ability to
size the memory ranges affected by intrinsics. This aids the compiler in
eliminating redundant load and stores in dynamic dispatching by enabling
alias-analysis optimizations.