[AArch64] Updated bigendian buildvector tests

As suggested by @efriedma on D49262 - changed the extractelement to a store to prevent SimplifyDemandedVectorElts from simplifying the build vectors - this keeps the immediate generation which was the point of the tests.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@336981 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed