[llvm] [CSSPGO] Return error_code for missing probe profile (PR #102085)

[Lei Wang via llvm-commits]

wlei-llvm wrote:

> > Given that pre-link sample-profile is before inline
> 
> the profile annotation part (`computeAndPropagateWeights`) is actually done after the inlining in sample loader itself, so technically speaking, the part you are changing here is after inlining for pre-link.

Yeah, but for pre-link sample loader, we only do inlining when we find the samples, so later we should always find the samples(can't repro the NULL return value)

https://github.com/llvm/llvm-project/pull/102085