[Bug tree-optimization/93249] [10 Regression] wrong code with __builtin_strncpy() copying empty string

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93249

--- Comment #4 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Created attachment 47650
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=47650&action=edit
gcc10-pr93249.patch

Untested fix.