[Bug target/79671] [7 Regression] mapnik miscompilation on armv7hl since r235622

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79671

--- Comment #58 from Jonathan Wakely <redi at gcc dot gnu.org> ---
But this seemingly equivalent code doesn't work:

  this->functor = static_cast<function_buffer&>(f.functor);