amd/llvm: transition to LLVM opaque pointers
See LLVM Opaque pointers: https://llvm.org/docs/OpaquePointers.html https://llvm.org/devmtg/2015-10/slides/Blaikie-OpaquePointerTypes.pdf
This fixes the deprecation warnings on LLVMBuildCall LLVMBuildLoad LLVMBuildGEP etc, which are replaced in LLVM by variants taking an explicit operation type instead of deriving the type from the pointer type.
In this MR we address the LLVM warnings in src/amd/llvm.
Edited by Mihai Preda