[clang] [RISCV] Set __GCC_CONSTRUCTIVE_SIZE/__GCC_DESTRUCTIVE_SIZE to 64 for riscv64 (PR #162986)

[Pengcheng Wang via cfe-commits]

wangpc-pp wrote:

We found this issue accidentally. I don't know if we should document this in psabi or elsewhere, but I think the GCC should change it as well. cc @kito-cheng 

https://github.com/llvm/llvm-project/pull/162986