[llvm] [MC][ELF] Fix printing group signature symbols. (PR #112543)

[Ivan Kosarev via llvm-commits]

kosarev wrote:

@MaskRay If this needs a test, can you give some pointers as to what it might look like and where we would want it, please? Not quite my area.

https://github.com/llvm/llvm-project/pull/112543