clang -O2 -Wall -Wextra -Werror=implicit-function-declaration sys_mman/posix_typed_mem_open.c -o sys_mman/posix_typed_mem_open -D_GNU_SOURCE -D_BSD_SOURCE -D_ALL_SOURCE -D_DEFAULT_SOURCE -lm -lintl sys_mman/posix_typed_mem_open.c:18:2: error: implicit declaration of function 'posix_typed_mem_open' is invalid in C99 [-Werror,-Wimplicit-function-declaration] posix_typed_mem_open("", 0, 0); ^ 1 error generated.