[SLPVectorizer] minor tweaks around lambdas for compatibilty with older compilers#122348

AlexMaclean merged 2 commits intollvm:mainllvm/llvm-project:mainfrom

AlexMaclean:dev/amaclean/upstream-slpvect-refactorAlexMaclean/llvm-project:dev/amaclean/upstream-slpvect-refactorCopy head branch name to clipboard