cc -O2 -pipe  -pthread  -Wall -Wextra -Werror=implicit-function-declaration stdlib/qsort_r.c -o stdlib/qsort_r -D_GNU_SOURCE -D_BSD_SOURCE -D_ALL_SOURCE -D_DEFAULT_SOURCE  -lm -lpthread 
stdlib/qsort_r.c:21:2: error: call to undeclared function 'qsort_r'; ISO C99 and later do not support implicit function declarations [-Werror,-Wimplicit-function-declaration]
        qsort_r(numbers, sizeof(numbers) / sizeof(int), sizeof(int), compare_int_r,
        ^
stdlib/qsort_r.c:21:2: note: did you mean 'qsort'?
/usr/include/stdlib.h:121:7: note: 'qsort' declared here
void     qsort(void *, size_t, size_t, int (*)(const void *, const void *));
         ^
1 error generated.