[X86][LoopVectorize] Replace -mcpu=skylake-avx512 with -mattr=avx512f in some tests that failed when experimenting with defaulting to -mprefer-vector-width=256 for skylake-avx512.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@348063 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed