[llvm] Decompose gep of complex type struct to its element type (PR #107848)

[via llvm-commits]

vfdff wrote:

Thank you for your advice, so I need to adjust to **i8 GEP** directly here too? 
I've tried to adjust directly to i8 GEP before, but I see some test cases regression, then I'll see why.  

https://github.com/llvm/llvm-project/pull/107848