[AVX512] Make vextract*x4/vinsert*x4 tests check for the index as well

Extend test so that it provides coverage for the next commit.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@218479 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed