[llvm] [BOLT] Detect Linux kernel version if the binary is a Linux kernel (PR #119088)

[via llvm-commits]

FLZ101 wrote:

> I don't mind the direction in general, but if you can add a subsequent patch showing how you want to use the functionality, that would be great.

@dcci An example usage of `LinuxKernelVersion` is included in https://github.com/llvm/llvm-project/pull/120929.

https://github.com/llvm/llvm-project/pull/119088