[llvm] [ADT] Deprecate the redirection from SmallSet to SmallPtrSet (Take 2) (PR #155078)

[Ben Langmuir via llvm-commits]

benlangmuir wrote:

I'm seeing gcc warn unconditionally ([godbolt link](https://godbolt.org/#g:!((g:!((g:!((h:codeEditor,i:(filename:'1',fontScale:14,fontUsePx:'0',j:1,lang:c%2B%2B,selection:(endColumn:66,endLineNumber:3,positionColumn:66,positionLineNumber:3,selectionStartColumn:66,selectionStartLineNumber:3,startColumn:66,startLineNumber:3),source:'template%3Ctypename+T%3E+struct+__attribute__((deprecated))+Deprecated+%7B%7D%3B%0Atemplate%3Ctypename+T%3E+struct+Top+%7B%7D%3B%0Atemplate%3Ctypename+P%3E+struct+Top%3CP+*%3E+:+public+Deprecated%3CP+*%3E+%7B%7D%3B'),l:'5',n:'0',o:'C%2B%2B+source+%231',t:'0')),k:33.567565730202034,l:'4',n:'0',o:'',s:0,t:'0'),(g:!((h:compiler,i:(compiler:g152,filters:(b:'0',binary:'1',binaryObject:'1',commentOnly:'0',debugCalls:'1',demangle:'0',directives:'0',execute:'1',intel:'0',libraryCode:'0',trim:'1',verboseDemangling:'0'),flagsViewOpen:'1',fontScale:14,fontUsePx:'0',j:1,lang:c%2B%2B,libs:!(),options:'-Wall',overrides:!(),selection:(endColumn:1,endLineNumber:1,positionColumn:1,positionLineNumber:1,selectionStartColumn:1,selectionStartLineNumber:1,startColumn:1,startLineNumber:1),source:1),l:'5',n:'0',o:'+x86-64+gcc+15.2+(Editor+%231)',t:'0')),k:33.496897574164045,l:'4',n:'0',o:'',s:0,t:'0'),(g:!((h:output,i:(compilerName:'x86-64+gcc+15.2',editorid:1,fontScale:14,fontUsePx:'0',j:1,wrap:'1'),l:'5',n:'0',o:'Output+of+x86-64+gcc+15.2+(Compiler+%231)',t:'0')),k:32.93553669563393,l:'4',n:'0',o:'',s:0,t:'0')),l:'2',n:'0',o:'',t:'0')),version:4)) but clang only warn if the template is used.  Maybe this should be reverted?

https://github.com/llvm/llvm-project/pull/155078