[llvm] feat: fix big endian shuffle vector miscompile (PR #68673)

[via llvm-commits]

hstk30-hw wrote:

> Also - AArch64ISD::NVCAST == ISD::BITCAST under LE, so it can be used in both cases.

Replace `ISD::BITCAST` to `AArch64ISD::NVCAST` simply will let this commit:  https://github.com/llvm/llvm-project/commit/62fc58a61d153daa015b9e22b0c386c74a5f7076 not work.

Check it plz. @davemgreen 

https://github.com/llvm/llvm-project/pull/68673