[clang] [libc] [llvm] Reapply "[AMDGPU] Use COV6 by default (#118515)" (PR #130963)

[Matt Arsenault via llvm-commits]

================
@@ -332,6 +332,8 @@ Target Specific Changes
 AMDGPU Support
 ^^^^^^^^^^^^^^
 
+- Bump the default code object version to 6. ROCm 6.3 is required to run any program compiled with COV6.
----------------
arsenm wrote:

We probably should have a defined policy for version support. It's also a long standing frustration of mine that we do not version the amdhsa OS to correspond to the rocm runtime version 

https://github.com/llvm/llvm-project/pull/130963