[clang] [llvm] [clang][CodeGen] `used` globals && the payloads for global ctors & dtors are globals (PR #93601)

[Alexander Richardson via llvm-commits]

https://github.com/arichardson commented:

Commit title needs updating to only refer to used metadata. A few wording suggestions inline.

https://github.com/llvm/llvm-project/pull/93601