[clang] let Neon builtin function accept a const variable (PR #144625)

[Eli Friedman via cfe-commits]

https://github.com/efriedma-quic commented:

Needs regression tests (in clang/test/Sema/).  For NEON intrinsics, and whatever other classes of intrinsics are affected by this.

Please add a reference to the issue in the commit message, like "fixes #144625" (the initial comment on the pull request will become the commit message when it's merged).

https://github.com/llvm/llvm-project/issues/139033#issuecomment-2868006401 suggested we want to warn when we do non-standard folding like this.

https://github.com/llvm/llvm-project/pull/144625