[amdgpu] Default to code object v3
v4 is not yet readily available, and doesn't appear
to be implemented in the back end
Reviewed By: t-tye, yaxunl
Differential Revision: https://reviews.llvm.org/D93258
[NFC] Use regex for code object version in hip tests
Extracted from D93258. Makes tests robust to changes in default
code object version.
Reviewed By: t-tye
Differential Revision: https://reviews.llvm.org/D93398