[libunwind] [RISCV] Allow libunwind to build for rv32e (PR #98855)

[Louis Dionne via cfe-commits]

https://github.com/ldionne commented:

This seems reasonable to me, but I have basically no knowledge of risvc or the rv32e ABI so I'll let someone else stamp this.

https://github.com/llvm/llvm-project/pull/98855