[Bug libstdc++/86590] Codegen is poor when passing std::string by value with _GLIBCXX_EXTERN_TEMPLATE undefined

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86590

--- Comment #27 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Created attachment 44415
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=44415&action=edit
gcc9-p0595r1.patch

Untested patch that passes the testcase in P0595R1.