[expr.unary.op] Add a note about dereferencing a dangling pointer#8130

tkoeppe merged 2 commits intocplusplus:maincplusplus/draft:mainfrom

dangelog:clarify-expr-unary-op-dangling-ptrdangelog/cplusplusdraft:clarify-expr-unary-op-dangling-ptrCopy head branch name to clipboard