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/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()