Backport GCC 8 fixes to 2.1

Backported the minimal set of changes required to build 2.1 with GCC
8. The format-truncation and format-overflow warnings are disabled instead
of fixed in 2.1 to remove duplication of effort that was already done in
2.2 (the commit doesn't cherry-pick cleanly).

server/core/gateway.cc

@@ -39,12 +39,12 @@
 
 #include <execinfo.h>
 #include <ftw.h>
-#include <getopt.h>
 #include <stdlib.h>
 #include <string.h>
 #include <strings.h>
 #include <time.h>
 #include <unistd.h>
+#include <getopt.h>
 
 #include <ini.h>
 #include <openssl/opensslconf.h>

server/core/maxpasswd.c

@@ -28,6 +28,7 @@
 #include <stdio.h>
 #include <errno.h>
 #include <sys/stat.h>
+#include <getopt.h>
 
 #include <maxscale/paths.h>
 #include <maxscale/log_manager.h>

server/modules/routing/avrorouter/CMakeLists.txt

@@ -6,6 +6,7 @@ if(AVRO_FOUND AND JANSSON_FOUND)
   set_target_properties(avrorouter PROPERTIES LINK_FLAGS -Wl,-z,defs)
   target_link_libraries(avrorouter maxscale-common ${JANSSON_LIBRARIES} ${AVRO_LIBRARIES} maxavro sqlite3 lzma)
   install_module(avrorouter core)
+  set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -Wno-format-overflow -Wno-format-truncation")
 
   if (BUILD_TESTS)
     add_subdirectory(test)

server/modules/routing/binlogrouter/CMakeLists.txt

@@ -9,6 +9,8 @@ target_link_libraries(maxbinlogcheck maxscale-common ${PCRE_LINK_FLAGS} uuid)
 
 install_executable(maxbinlogcheck core)
 
+set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -Wno-format-overflow -Wno-format-truncation")
+
 if(BUILD_TESTS)
   add_subdirectory(test)
 endif()