nokogiriを更新したらRubyを実行するたびに「Ignoring」と毎回怒られるようになった

nokogiriを更新すると毎回このようにIgnoringが出てくるようになった。

Ignoring childprocess-2.0.0 because its extensions are not built. Try: gem pristine childprocess --version 2.0.0
Ignoring childprocess-1.0.1 because its extensions are not built. Try: gem pristine childprocess --version 1.0.1
Ignoring ed25519-1.2.4 because its extensions are not built. Try: gem pristine ed25519 --version 1.2.4
Ignoring escape_utils-1.1.1 because its extensions are not built. Try: gem pristine escape_utils --version 1.1.1
Ignoring ffi-1.11.3 because its extensions are not built. Try: gem pristine ffi --version 1.11.3
Ignoring ffi-1.11.2 because its extensions are not built. Try: gem pristine ffi --version 1.11.2
Ignoring ffi-1.11.1 because its extensions are not built. Try: gem pristine ffi --version 1.11.1
Ignoring ffi-1.11.0 because its extensions are not built. Try: gem pristine ffi --version 1.11.0
Ignoring ffi-1.9.25 because its extensions are not built. Try: gem pristine ffi --version 1.9.25
Ignoring ffi-1.9.23 because its extensions are not built. Try: gem pristine ffi --version 1.9.23
Ignoring ffi-1.9.18 because its extensions are not built. Try: gem pristine ffi --version 1.9.18
Ignoring greenmat-3.2.2.4 because its extensions are not built. Try: gem pristine greenmat --version 3.2.2.4
Ignoring json-2.2.0 because its extensions are not built. Try: gem pristine json --version 2.2.0
Ignoring json-1.8.6 because its extensions are not built. Try: gem pristine json --version 1.8.6
Ignoring kgio-2.11.3 because its extensions are not built. Try: gem pristine kgio --version 2.11.3
Ignoring kgio-2.11.2 because its extensions are not built. Try: gem pristine kgio --version 2.11.2
Ignoring msgpack-1.3.1 because its extensions are not built. Try: gem pristine msgpack --version 1.3.1
Ignoring msgpack-1.3.0 because its extensions are not built. Try: gem pristine msgpack --version 1.3.0
Ignoring msgpack-1.2.10 because its extensions are not built. Try: gem pristine msgpack --version 1.2.10
Ignoring msgpack-1.2.6 because its extensions are not built. Try: gem pristine msgpack --version 1.2.6
Ignoring msgpack-1.2.4 because its extensions are not built. Try: gem pristine msgpack --version 1.2.4
Ignoring mysql2-0.5.1 because its extensions are not built. Try: gem pristine mysql2 --version 0.5.1
Ignoring mysql2-0.4.10 because its extensions are not built. Try: gem pristine mysql2 --version 0.4.10
Ignoring mysql2-0.3.20 because its extensions are not built. Try: gem pristine mysql2 --version 0.3.20
Ignoring mysql2-0.3.18 because its extensions are not built. Try: gem pristine mysql2 --version 0.3.18

解決策

gem pristine --all
を複数回、Igonorが消えるまで実行する。

途中でmysqlに関するエラーがでたが、アンインストールし、再インストールすると解消された