Description:
------------
When compiling the errno.h file included in snmp.c file has also include from not standard sys/errno.h for historic reasons. All other errno.h files included elsewhere in PHP code are included using <errno.h> which is also POSIX compliant.

Actual result:
--------------
In file included from /build/main/php7.2/src/php-7.2.0alpha3/ext/snmp/snmp.c:51:0:
/usr/include/sys/errno.h:1:2: warning: #warning redirecting incorrect #include <sys/errno.h> to <errno.h> [-Wcpp]
 #warning redirecting incorrect #include <sys/errno.h> to <errno.h>
  ^~~~~~~
/build/main/php7.2/src/php-7.2.0alpha3/ext/snmp/snmp.c: In function 'zm_startup_snmp':
/build/main/php7.2/src/php-7.2.0alpha3/ext/snmp/snmp.c:2328:34: warning: assignment from incompatible pointer type [-Wincompatible-pointer-types]
  php_snmp_object_handlers.get_gc = php_snmp_get_gc;