[clang] [clang] Add information about lld presence in RISCVToolchain. (PR #68904)

[Bushev Dmitry via cfe-commits]

dybv-sc wrote:

Encountered code formatting check failure seems to be not reproducible locally:

```
$ git-clang-format --diff 7025ff6fa3dfe2ce8d3d7fcb0ec9de9a357d2c6f 087d22970d1d2eea6dd0dd79eedd49ed69bc49c3 -- clang/lib/Driver/ToolChains/RISCVToolchain.cpp clang/lib/Driver/ToolChains/RISCVToolchain.h clang/test/Driver/riscv64-toolchain.c
$ echo $?
0
```

https://github.com/llvm/llvm-project/pull/68904