256-bit floating-point SIMD primitives unnecessarily require `-mavx2`

Summary

When using 256-bit floating-point SIMD primitives (i.e. FloatX8# or DoubleX4#), GHC requires -mavx2. -mavx should be sufficient.

Steps to reproduce

-- Test.hs
{-# LANGUAGE MagicHash #-}
{-# LANGUAGE UnboxedTuples #-}
import GHC.Exts

main = do
  let (# x0, x1, x2, x3 #) = unpackDoubleX4# (negateDoubleX4# (packDoubleX4# (# 0.0##, 1.1##, 2.2##, 3.3## #)))
  print (D# x0, D# x1, D# x2, D# x3)

$ _build/stage1/bin/ghc -fllvm -mavx Test.hs
[1 of 2] Compiling Main             ( Test.hs, Test.o )

<no location info>: error:
    sorry! (unimplemented feature or known bug)
  GHC version 9.9.20231124:
        256-bit wide integer SIMD vector instructions require at least -mavx2.

$ _build/stage1/bin/ghc -fllvm -mavx2 Test.hs
[1 of 2] Compiling Main             ( Test.hs, Test.o )
[2 of 2] Linking Test

Expected behavior

ghc -fllvm -mavx Test.hs should compile.

Environment

• GHC version used: 9.9.20231124 (34d86315)
• Operating System: Ubuntu 22.04
• System Architecture: x86-64