clang -O2  -Wall -Wextra -Werror -Wno-error=deprecated -Wno-error=deprecated-declarations math/M_SQRT1_3.c -o math/M_SQRT1_3 -D_POSIX_C_SOURCE=202405L  -lm  -lintl
math/M_SQRT1_3.c:8:21: error: use of undeclared identifier 'M_SQRT1_3'
double  const foo = M_SQRT1_3;
                    ^
1 error generated.