[llvm] [VPlan] Use pragma pack(1) for VPIRFlags on AIX. (PR #184687)

[Florian Hahn via llvm-commits]

fhahn wrote:

@midhuncodes7 is this with a clean build? So far looks like this commit is fine on the build bots.

https://github.com/llvm/llvm-project/pull/184687