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