Needs to include stdio.h in nginx/auto/feature for this to work

https://github.com/SpiderLabs/ModSecurity-nginx/blob/2497e6ac654d0b117b9534aa735b757c6b11c84f/config#L15

nginx src version: 1.20.2

When I was trying to compile the nginx connector module, nginx configure was complaining about libmodsecurity not found. Command line I was using:

./configure --with-http_ssl_module --with-threads  --with-compat --add-dynamic-module=/usr/local/opt/ModSecurity-nginx/

I checked nginx/objs/autoconf.err and this is in it

----------------------------------------
checking for ModSecurity library in "/usr/local/opt/ModSecurity/src/.libs/" and "/usr/local/opt/ModSecurity/headers/" (specified by the MODSECURITY_LIB and MODSECURITY_INC env)

objs/autotest.c:6:5: error: implicitly declaring library function 'printf' with type 'int (const char *, ...)' [-Werror,-Wimplicit-function-declaration]
    printf("hello");;
    ^
objs/autotest.c:6:5: note: include the header <stdio.h> or explicitly provide a declaration for 'printf'
1 error generated.
----------
#include <sys/types.h>
#include <unistd.h>
#include <modsecurity/modsecurity.h>

int main(void) {
    printf("hello");;
    return 0;
}

So I think you need to either set $NGX_INCLUDE_UNISTD_H or not use printf

Start with the linked config file at config#L15 and inspect how nginx/auto/feature generates the compile check shown in objs/autoconf.err. Re-run the provided nginx 1.20.2 configure command, then confirm the connector configure step no longer fails on the undeclared printf call.