try fix include path for check header

Author: mcarbonneaux

configure.ac

@@ -40,6 +40,7 @@ AC_CHECK_ZABBIX_DIR
 AC_CHECK_HEADERS(sysinc.h common/zbxsysinc.h)
 AC_SUBST([MODULE_NAME])
 AC_SUBST([CFLAGS])
+AC_SUBST([CPPFLAGS])
 AC_SUBST([LDFLAGS])
 AC_SUBST([LIBS])
 AC_SUBST([prefix])

m4/ax_zabbix.m4

@@ -39,7 +39,7 @@ AC_HELP_STRING([--with-zabbix-include@<:@=DIR@:>@], [Zabbix include directory])
       AC_MSG_ERROR( $with_zabbix_include not found. )
     fi
     ZABBIX_INC_DIR=$with_zabbix_include
-    AP_INCLUDE_DIR="-I$ZABBIX_INC_DIR"
+    CPPFLAGS="-I$ZABBIX_INC_DIR"
   fi
 
   AC_SUBST([ZABBIX_INC_DIR])