ruby-filemagic -v 0.6.1 Gem::Ext::BuildError: ERROR: Failed to build gem native extension.　の解決方法

備忘録です。
` bundle install ` が通らずRubyのバージョンを変えてやってみたのですが、あと一歩のところでエラーが出ました。
Rubyのバージョンは2.3.1、bundlerのバージョンはRuby2.3.1に対応するバージョンです。

```
$ bundle install

Fetching gem metadata from https://rubygems.org/............
Fetching version metadata from https://rubygems.org/..
Fetching dependency metadata from https://rubygems.org/.
Resolving dependencies................................
Using rake 10.4.2
Using i18n 0.7.0
Using json 1.8.2
Using minitest 5.5.0
Using thread_safe 0.3.4
Using builder 3.2.2
Using erubis 2.7.0
Using rack 1.5.2
Using mime-types 2.4.3
Using sass 3.2.19
Using thor 0.19.1
Using coffee-script-source 1.8.0
Using execjs 2.2.2
Using formtastic_i18n 0.6.0
Using arel 5.0.1.20140414130214
Using hike 1.2.3
Using multi_json 1.10.1
Using tilt 1.4.1
Using addressable 2.3.8
Using ast 2.3.0
Using awesome_print 1.2.0
Using jmespath 1.3.1
Using bcrypt 3.1.9
Using coderay 1.1.0
Using debug_inspector 0.0.2
Using bundler 1.13.6
Using columnize 0.9.0
Using debugger-linecache 1.2.0
Using slop 3.6.0
Using cancancan 1.13.1
Using chunky_png 1.3.4
Using orm_adapter 0.5.0
Using multipart-post 2.0.0
Using elasticsearch-dsl 0.1.4
Using hashie 3.4.6
Using libv8 3.16.14.15
Using method_source 0.8.2
Using mysql2 0.3.18
Using powerpack 0.1.1
Using yard 0.8.7.6
Using rainbow 2.1.0
Using ref 1.0.5
Using ruby-progressbar 1.8.1
Using unicode-display_width 1.1.1
Installing ruby-filemagic 0.6.1 with native extensions
Using rubyzip 1.1.7
Using spring 1.2.0
Using sqlite3 1.3.10
Using uuidtools 2.1.5
Using rdoc 4.2.0
Using tzinfo 1.2.2
Using rack-test 0.6.2
Using warden 1.2.3
Using mail 2.6.3
Using bourbon 3.2.4
Using coffee-script 2.3.0
Using uglifier 2.6.0
Using elasticsearch-api 5.0.0
Using sprockets 2.12.3
Using fastimage 1.7.0
Using parser 2.3.1.4
Using aws-sdk-core 2.3.19
Using better_errors 2.0.0
Using binding_of_caller 0.7.2
Using byebug 3.5.1
Using rqrcode 0.7.0
Using faraday 0.9.2
Using pry 0.10.1
Using therubyracer 0.12.2
Gem::Ext::BuildError: ERROR: Failed to build gem native extension.

current directory:
/Users/fndm40/JinsPaintWEBAdmin/jinspaintwebadmin/web-admin/vendor/bundle/ruby/2.3.0/gems/ruby-filemagic-0.6.1/ext/filemagic
/Users/fndm40/.rbenv/versions/2.3.1/bin/ruby -r
./siteconf20170302-11345-1879bea.rb extconf.rb
checking for magic_open() in -lmagic... no
*** ERROR: missing required library to compile this module
*** extconf.rb failed ***
Could not create Makefile due to some reason, probably lack of necessary
libraries and/or headers.  Check the mkmf.log file for more details.  You may
need configuration options.

Provided configuration options:
	--with-opt-dir
	--without-opt-dir
	--with-opt-include
	--without-opt-include=${opt-dir}/include
	--with-opt-lib
	--without-opt-lib=${opt-dir}/lib
	--with-make-prog
	--without-make-prog
	--srcdir=.
	--curdir
	--ruby=/Users/fndm40/.rbenv/versions/2.3.1/bin/$(RUBY_BASE_NAME)
	--with-magic-dir
	--without-magic-dir
	--with-magic-include
	--without-magic-include=${magic-dir}/include
	--with-magic-lib
	--without-magic-lib=${magic-dir}/lib
	--with-magiclib
	--without-magiclib

To see why this extension failed to compile, please check the mkmf.log which
can be found here:

/Users/fndm40/JinsPaintWEBAdmin/jinspaintwebadmin/web-admin/vendor/bundle/ruby/2.3.0/extensions/x86_64-darwin-15/2.3.0-static/ruby-filemagic-0.6.1/mkmf.log

extconf failed, exit code 1

Gem files will remain installed in
/Users/fndm40/JinsPaintWEBAdmin/jinspaintwebadmin/web-admin/vendor/bundle/ruby/2.3.0/gems/ruby-filemagic-0.6.1
for inspection.
Results logged to
/Users/fndm40/JinsPaintWEBAdmin/jinspaintwebadmin/web-admin/vendor/bundle/ruby/2.3.0/extensions/x86_64-darwin-15/2.3.0-static/ruby-filemagic-0.6.1/gem_make.out

An error occurred while installing ruby-filemagic (0.6.1), and
Bundler cannot continue.
Make sure that `gem install ruby-filemagic -v '0.6.1'` succeeds before
bundling.
```

gemの `ruby-filemagic`　に問題があるようです。
ちなみに `gem install ruby-filemagic -v '0.6.1'` をやっても同じようなエラーが出ました。

```
Could not create Makefile due to some reason, probably lack of necessary
libraries and/or headers.  Check the mkmf.log file for more details.  You may
need configuration options.
```

と書いているので mkmf.logファイルを探して参照してみます。

```
$ find ~/.rbenv | grep ruby-filemagic | grep mkmf.log

/Users/fndm40/.rbenv/versions/2.3.1/lib/ruby/gems/2.3.0/extensions/x86_64-darwin-15/2.3.0-static/ruby-filemagic-0.6.1/mkmf.log

```

場所を特定したのでvimでファイルを開きます。

```
$ vim /Users/fndm40/.rbenv/versions/2.3.1/lib/ruby/gems/2.3.0/extensions/x86_64-darwin-15/2.3.0-static/ruby-filemagic-0.6.1/mkmf.log

```

中身を見ましたが、全く意味がわからない。
中身はC言語で書かれているのですが、エラーがいろんなところに出ている。
困った。
そもそも `gem install ruby-filemagic`　でつまずいてる人がいないか調べてみたら、いました！

```
$ brew install libmagic
```
を行い

```
$ gem install ruby-filemagic -v '0.6.1'
$ bundle install

```

をやったら解決。
やっと開発環境を整えられる…。