[Bug target/92055] [avr] Support 64-bit double

[gjl at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92055

--- Comment #3 from Georg-Johann Lay <gjl at gcc dot gnu.org> ---
Created attachment 47030
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=47030&action=edit
double64-4.diff: patch that also supports --with-long-double64