https://gcc.gnu.org/bugzilla/show_bug.cgi?id=51146
--- Comment #10 from Andrew Pinski <pinskia at gcc dot gnu.org> --- Starting in GCC 8, we warn about this: <source>:5:5: warning: built-in function 'clog' declared as non-function [-Wbuiltin-declaration-mismatch] int clog=0; ^~~~ I noticed that LLVM's libc++ does not call clog but just log.