Proposed resolution:

• Add a footnote in 17.2 [support.types] paragraph 5:

  [Footnote: Note that offsetof is required to work as specified even if unary operator& is overloaded for any of the types involved.]

• Add a footnote in 17.14 [support.runtime] paragraph 3:

  [Footnote: Note that va_start is required to work as specified even if unary operator& is overloaded for the type of parmN.]