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

[Wang Pengcheng via cfe-commits]

wangpc-pp wrote:

> short version: GCC isn't change. long version: GCC's configure script isn't change, it's configure script in riscv-gnu-toolchain

So why is there a difference between GCC and riscv-gnu-toolchain? If we set `with_abi` to lp64f, what is the behavior?
> 
> But I don't have strong opinion on this change since I believe user should explicitly specify that, otherwise it's really to screw up to select multi-lib or portability issue between different compilers.



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