[clang] [RISCV] Fix incorrect check prefix in riscv32-toolchain.c and riscv64-toolchain.c. NFC. (PR #109390)

[Fangrui Song via cfe-commits]

https://github.com/MaskRay approved this pull request.

You can use `[test]` instead of `. NFC.`

`-SAME: ` is preferred when testing a string on the same line 

https://github.com/llvm/llvm-project/pull/109390