[llvm] [AArch64] Fix vectorToScalarBitmask BE (#156312) (PR #156314)

[Giuseppe Cesarano via llvm-commits]

GiuseppeCesarano wrote:

Applying volatile to the vector load and store seems to force the compiler to emit the extraction mask, even at higher levels of optimization. Now, the test doesn't depend on -O0 anymore. 

Unfortunately, it doesn't seem to be a test that specifically wants to generate this mask, so a completely new one is needed.

If other changes are necessary, please let me know.

https://github.com/llvm/llvm-project/pull/156314