gcc -pthread   -Wall -Wextra -Werror -Wno-error=deprecated -Wno-error=deprecated-declarations math/M_PI_2l.c -o math/M_PI_2l -D_POSIX_C_SOURCE=202405L -lm -lpthread -lrt -lxnet  -lsocket -latomic
math/M_PI_2l.c:8:26: error: ‘M_PI_2l’ undeclared here (not in a function); did you mean ‘M_PI_2’?
    8 | long double  const foo = M_PI_2l;
      |                          ^~~~~~~
      |                          M_PI_2