[llvm] [clang] [clang][RISCV] Change default abi when only have f extension but no d extension (PR #73489)

[Wang Pengcheng via cfe-commits]

https://github.com/wangpc-pp approved this pull request.

I have similar patch before: https://reviews.llvm.org/D125947, so it LGTM as GCC's default behavior has changed. :-)
But please wait for others' opinions.

https://github.com/llvm/llvm-project/pull/73489