cc -pipe -O   -pthread  -Wall -Wextra -Werror -Wno-error=deprecated -Wno-error=deprecated-declarations math/M_SQRT2l.c -o math/M_SQRT2l -D_POSIX_C_SOURCE=202405L  -lm -lpthread -lrt  -lrt -lcrypt
math/M_SQRT2l.c:8:26: error: 'M_SQRT2l' undeclared here (not in a function); did you mean 'M_SQRT2'?
 long double  const foo = M_SQRT2l;
                          ^~~~~~~~
                          M_SQRT2