[Bug libstdc++/114958] use __builtin_shufflevector for std::experimental::simd split and concat (at least the common cases) to enable better optimizations

[mkretz at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114958

--- Comment #7 from Matthias Kretz (Vir) <mkretz at gcc dot gnu.org> ---
the regression is now PR115247