[Bug c/91092] Error on implicit function declarations by default

[sam at gentoo dot org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91092

--- Comment #21 from Sam James <sam at gentoo dot org> ---
Followers of this bug may be interested to learn:
1. Clang has made this change in LLVM 15 (as well as some other related
changes:
https://releases.llvm.org/15.0.0/tools/clang/docs/ReleaseNotes.html#improvements-to-clang-s-diagnostics);

2. There's discussion ongoing at
https://discourse.llvm.org/t/configure-script-breakage-with-the-new-werror-implicit-function-declaration/65213
wrt the breakage to configure scripts.