[Bug ipa/59948] Optimize std::function

[hubicka at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59948

--- Comment #3 from Jan Hubicka <hubicka at gcc dot gnu.org> ---
The code in fold-const for nonzero check is really broken.  I have somewerhe
WIP symtab patch for doing this, but it is not completely trivial to hook it
into fold-const when symtab is not built yet - just as in this case and in some
cases for LTO you really want to know if symbol is defined...