cc -O2 -pipe  -pthread  -Wall -Wextra -Werror -Wno-error=deprecated -Wno-error=deprecated-declarations math/M_SQRT1_3l.c -o math/M_SQRT1_3l -D_POSIX_C_SOURCE=202405L  -lm -lpthread 
math/M_SQRT1_3l.c:8:26: error: use of undeclared identifier 'M_SQRT1_3l'
long double  const foo = M_SQRT1_3l;
                         ^
1 error generated.