[llvm] [ADT][NFC] Move FoldingSetBase definition lower in the file (PR #172503)

[Jakub Kuderski via llvm-commits]

kuhar wrote:

> It would be surprising to me that this PR caused the failure. I've triggered a rebuild: https://lab.llvm.org/buildbot/#/buildrequests/6558151?redirect_to_build=true.
> 
> UPDATE: the test now passes since [cb43ae4](https://github.com/llvm/llvm-project/commit/cb43ae446fa0e31fa6f1e4d89e453dc91ce14ce3).

probably unrelated to your PR

https://github.com/llvm/llvm-project/pull/172503