"Unused function" build failure(s) — clang 12.0.1

-Wall -Werror are including the option -Wunused-function. Without not the case with g++
namespace { 
   void dummy_for_semicolon_do_not_use();
}
PackageVersionSupposed error messageFull log Bug report
libcerf 1.3-2.1w_of_z.c:79:21: error: unused function 'cpolar' [-Werror,-Wunused-function] Log

1 errors