clang -O2  -Wall -Wextra -Werror=implicit-function-declaration signal/str2sig.c -o signal/str2sig -D_GNU_SOURCE -D_BSD_SOURCE -D_ALL_SOURCE -D_DEFAULT_SOURCE  -lm  -lintl
signal/str2sig.c:10:7: error: implicit declaration of function 'str2sig' is invalid in C99 [-Werror,-Wimplicit-function-declaration]
        if ( str2sig("USR1", &signo) < 0 )
             ^
1 error generated.