[llvm] [Object][AMDGPU] Support REL relocations (PR #143966)

[Fangrui Song via llvm-commits]

MaskRay wrote:

Looks good, though ideally there is some description why you need REL for static relocations. REL static relocations are constrained and turned out to be a bad choice for EM_ARM

https://github.com/llvm/llvm-project/pull/143966