[riscv] LLVM silently switches the ABI when target features are incorrect

For instance, if the ABI is set to "ilp32" but the "e" target feature is enabled, LLVM ends up actually using the "ilp32e" ABI. I don't think LLVM should just silently ignore the ABI we explicitly asked for.
Cc @beetrees

This is very similar to https://github.com/llvm/llvm-project/issues/110383 for ARM which was recently fixed.

Start by reproducing the RISC-V case described: an explicit "ilp32" ABI with the "e" target feature enabled. Compare the behavior and resolution in ARM issue 110383; done means LLVM no longer silently changes the requested ABI when target features are inconsistent.

Written by the indexing model from the issue text.