[llvm] [GSYM] Allow executable symtab symbols with unknown type (PR #119307)

[via llvm-commits]

itrofimow wrote:

This aims to fix the following problem: 
given a function `FZERO`, which somehow ends up having a zero size in resulting GSYM,
and a function `FUNKNOWN`, which instructions immediately follow `FZERO` and which symbol is of `ST_Unknown` type in symtab,
all lookups of `FUNKNOWN` addresses resolve into `FZERO` due to
1. `FUNKNOWN` not being present in the resulting GSYM (which this patch aims to change)
2. This logic https://github.com/llvm/llvm-project/blob/a1d71c36933e361f4561288d4a0e257432345483/llvm/lib/DebugInfo/GSYM/GsymReader.cpp#L282-L284

https://github.com/llvm/llvm-project/pull/119307