cc -O2 -pipe -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  -lstdthreads -lcrypt
math/M_SQRT2l.c:8:26: error: use of undeclared identifier 'M_SQRT2l'
    8 | long double  const foo = M_SQRT2l;
      |                          ^
1 error generated.