title: Package MagickCore was not found in the pkg-config search path
body: <p>I was trying to install <code>rmagick</code> and it always asks for <code>PKG_CONFIG_PATH</code> not configured. </p>
  
  <p>This happened multiple times to me, so I'm posting this as an issue and answering myself for anyone else facing same issue.</p>
  
  <pre><code>User-MacBook-Pro:rsscom macuser$ gem install rmagick -v '2.13.3'
  Building native extensions.  This could take a while...
  ERROR:  Error installing rmagick:
      ERROR: Failed to build gem native extension.
  
      /Users/macuser/.rvm/rubies/ruby-2.2.0/bin/ruby -r ./siteconf20160705-63310-klqxmw.rb extconf.rb
  checking for Ruby version &gt;= 1.8.5... yes
  checking for gcc... yes
  checking for Magick-config... yes
  checking for ImageMagick version &gt;= 6.4.9... yes
  Package MagickCore was not found in the pkg-config search path.
  Perhaps you should add the directory containing `MagickCore.pc'
  to the PKG_CONFIG_PATH environment variable
  No package 'MagickCore' found
  Package MagickCore was not found in the pkg-config search path.
  Perhaps you should add the directory containing `MagickCore.pc'
  to the PKG_CONFIG_PATH environment variable
  No package 'MagickCore' found
  Package MagickCore was not found in the pkg-config search path.
  Perhaps you should add the directory containing `MagickCore.pc'
  to the PKG_CONFIG_PATH environment variable
  No package 'MagickCore' found
  Package MagickCore was not found in the pkg-config search path.
  Perhaps you should add the directory containing `MagickCore.pc'
  to the PKG_CONFIG_PATH environment variable
  No package 'MagickCore' found
  checking for stdint.h... yes
  checking for sys/types.h... yes
  checking for wand/MagickWand.h... no
  
  Can't install RMagick 0.0.0. Can't find MagickWand.h.
  *** 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/macuser/.rvm/rubies/ruby-2.2.0/bin/$(RUBY_BASE_NAME)
  
  extconf failed, exit code 1
  
  Gem files will remain installed in /Users/macuser/.rvm/gems/ruby-2.2.0/gems/rmagick-2.13.3 for inspection.
  Results logged to /Users/macuser/.rvm/gems/ruby-2.2.0/extensions/x86_64-darwin-14/2.2.0-static/rmagick-2.13.3/gem_make.out
  </code></pre>