[llvm] [SampleProfile] Support Eytzinger layout in SecFuncOffsetTable (PR #213829)

[Snehasish Kumar via llvm-commits]

snehasish wrote:

The new Eytzinger offset array has only one slot per terminal function GUID, but a context-sensitive profile can contain multiple distinct "SampleContext"s ending in the same functiion. The existing "cs-sample.proftext" already has multiple contexts ending in "_Z8funcLeafi".

I think CS profiles need either the existing context-aware offset representation or an additional indirection that maps each function GUID to all of its context/offset entries. Please also add a round-trip test containing two distinct contexts with the same terminal function.

https://github.com/llvm/llvm-project/pull/213829