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

[Fangrui Song via llvm-commits]

MaskRay 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.

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