[llvm] [InlineAsm] wrap ConstraintCode in enum class NFC (PR #66003)

[Jan Patrick Lehr via llvm-commits]

jplehr wrote:

I believe this broke the AMDGPU OpenMP buildbot https://lab.llvm.org/buildbot/#/builders/193
Let me know if you need assistance in reproducing the issue.

https://github.com/llvm/llvm-project/pull/66003