[clang] [llvm] [PseudoProbe] Mix and reorder block and call probe ID in lexical order (PR #75092)

[via llvm-commits]

WenleiHe wrote:

We will need some protection against accidentally consuming old profile with new toolchain and vice versa. The cost of investigating mysterious perf regression can be high and we'd rather simply error out in those cases. Maybe consider some flag for `SecProfSummaryFlags` (also wondering if this needs to be per-function flag since technically some function/module can be compiled with old order while others with new order).

Can we gauge perf benefit of mixed order encoding? i.e. profile an old source rev (several weeks ago?) with both probe order, and build with new source rev using that old profile, then see how old vs new order compare in terms of perf and efficacy with incremental PGO. 

https://github.com/llvm/llvm-project/pull/75092