clang -O2  -Wall -Wextra -Werror=implicit-function-declaration time/clock_getcpuclockid.c -o time/clock_getcpuclockid -D_GNU_SOURCE -D_BSD_SOURCE -D_ALL_SOURCE -D_DEFAULT_SOURCE  -lm  -lintl
time/clock_getcpuclockid.c:12:15: error: implicit declaration of function 'clock_getcpuclockid' is invalid in C99 [-Werror,-Wimplicit-function-declaration]
        int errnum = clock_getcpuclockid(getpid(), &id);
                     ^
1 error generated.