Test PFA and document issues with Clang-19/20 versions

[tpatki]

[asantagata]

@spencer-gre and I experienced no issues running PFA on Clang-19. On Clang-20 there were several issues; here is a log of these on Tuo: pfa clang20 errors.txt

We made these changes (forked here) to PFA for successful run on Clang-20:

• Replaced every instance of createGlobalStringPtr in weaver/weave/perfflow_weave_common with createGlobalString. createGlobalStringPtr is deprecated as of Clang 20 and acts as a reference to createGlobalString which has a more generic type (https://llvm.org/doxygen/IRBuilder_8h_source.html#l02056); functionality is identical.

• In perfflow_weave_new_pass, replaced this block:

        PB.registerPipelineEarlySimplificationEPCallback(
            [&](ModulePassManager & MPM, auto)
        {
            MPM.addPass(NewWeavingPass());
            return true;
        }
        );

with this:

        PB.registerPipelineEarlySimplificationEPCallback(
            [&](ModulePassManager & MPM, OptimizationLevel OL, ThinOrFullLTOPhase TOFLTOP)
        {
            MPM.addPass(NewWeavingPass());
        }
        );

i.e., adding another parameter and removing the return to match the definition listed here: https://llvm.org/doxygen/llvm_2Passes_2PassBuilder_8h_source.html#l00505

With these changes, compilation is successful and all smoketests work.

[tpatki]

Closing with PR #199 and #200