[llvm] [BOLT, RISCV] Remove empty name special case from #68977 (PR #90004)

[Amir Ayupov via llvm-commits]

aaupov wrote:

> The premerge bot fails.
> 
> The reason is that `%clang` in `bolt/test/RISCV/fake-label-no-entry.c` expands to `/usr/bin/clang` instead of the just-built clang.

Let me look into that. It was done intentionally to reduce pre-merge builder load, but looks like there's no way around using trunk clang in BOLT testing.

https://github.com/llvm/llvm-project/pull/90004