[Bug middle-end/90959] hash_map can be copied but leads to a double-free after assignment

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90959

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
IIRC Jason added the constructor because the C++ FE does this.  I think
assignment is bad style so just delete that (or declare and not define for old
C++ - IIRC we do have = deleted macros in system.h or ansidecl.h?)