nokogiri Mac OS EI Caption install fail

[朱静朝]

Using pkg-config version 1.1.7

checking if the C compiler accepts ... yes

checking if the C compiler accepts -Wno-error=unused-command-line-argument-hard-error-in-future... no

Building nokogiri using packaged libraries.

Using mini_portile version 2.1.0

checking for iconv.h... yes

checking for gzdopen() in -lz... yes

checking for iconv... yes

what is mean？

checking if the C compiler accepts -Wno-error=unused-command-line-argument-hard-error-in-future... no

I have installed libxml2、libxslt

xcode-select --install is work for me

What am I to do？