gemを使ってgtk3をインストールしようとしたのですができませんでした
解決策をご教授願えませんか？ 出力は以下の通りです
少々長いのでレス分けます

C:/Ruby21-x64/bin/ruby.exe extconf.rb
checking for --enable-debug-build option... no
checking for -Wall option to compiler... yes
checking for -Waggregate-return option to compiler... yes
checking for -Wcast-align option to compiler... yes
checking for -Wextra option to compiler... yes
checking for -Wformat=2 option to compiler... yes
checking for -Winit-self option to compiler... yes
checking for -Wlarger-than-65500 option to compiler... yes
checking for -Wmissing-declarations option to compiler... yes
checking for -Wmissing-format-attribute option to compiler... yes
checking for -Wmissing-include-dirs option to compiler... yes
checking for -Wmissing-noreturn option to compiler... yes
checking for -Wmissing-prototypes option to compiler... yes
checking for -Wnested-externs option to compiler... yes
checking for -Wold-style-definition option to compiler... yes
checking for -Wpacked option to compiler... yes
checking for -Wp,-D_FORTIFY_SOURCE=2 option to compiler... yes
checking for -Wpointer-arith option to compiler... yes
checking for -Wswitch-default option to compiler... yes
checking for -Wswitch-enum option to compiler... yes
checking for -Wundef option to compiler... yes
checking for -Wout-of-line-declaration option to compiler... no
checking for -Wunsafe-loop-optimizations option to compiler... yes
checking for -Wwrite-strings option to compiler... yes
checking for rb_define_alloc_func() in ruby.h... no
checking for rb_block_proc() in ruby.h... no
checking for new allocation framework... yes