clang -O2  -Wall -Wextra -Werror=implicit-function-declaration sys_mman/posix_mem_offset.c -o sys_mman/posix_mem_offset -D_GNU_SOURCE -D_BSD_SOURCE -D_ALL_SOURCE -D_DEFAULT_SOURCE  -lm  -lintl
sys_mman/posix_mem_offset.c:21:2: error: implicit declaration of function 'posix_mem_offset' is invalid in C99 [-Werror,-Wimplicit-function-declaration]
        posix_mem_offset(NULL, 0, NULL, NULL, NULL);
        ^
1 error generated.