clang -O2  -Wall -Wextra -Werror -Wno-error=deprecated -Wno-error=deprecated-declarations math/M_SQRT2l.c -o math/M_SQRT2l -D_POSIX_C_SOURCE=202405L  -lm  -lintl
math/M_SQRT2l.c:8:26: error: use of undeclared identifier 'M_SQRT2l'
long double  const foo = M_SQRT2l;
                         ^
1 error generated.