[Bug gcov-profile/80435] Expose __gcov_flush to allow developers to dump coverage numbers on demand

[marxin at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80435

--- Comment #2 from Martin Liška <marxin at gcc dot gnu.org> ---
Created attachment 41211
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=41211&action=edit
Untested patch