Make test/CodeGen/ARM64/vector-insertion.ll explicitly select neon syntax

Change the command line vector-insertion.ll to explicitly set the neon syntax
to apple so that buildbots that default to other syntaxes won't fail.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@206502 91177308-0d34-0410-b5e6-96231b3b80d8