title: "rmagick" gem installation issue
body: <p>I am having issue while trying to install "rmagick" gem on centos. Following is the output I am having. Can anyone please help me identifying <strong>what package I am missing</strong>? I have installed all mentioned another stack-overflow thread: <a href="https://stackoverflow.com/questions/7431707/rmagick-install-error">RMagick install error</a></p>
  
  <pre><code>Building native extensions.  This could take a while...
  ERROR:  Error installing rmagick:
      ERROR: Failed to build gem native extension.
  
          /usr/local/bin/ruby 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
  checking for HDRI disabled version of ImageMagick... 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 2.13.2. 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=/usr/local/bin/ruby
  
  
  Gem files will remain installed in /usr/local/lib/ruby/gems/1.9.1/gems/rmagick-2.13.2 for inspection.
  Results logged to /usr/local/lib/ruby/gems/1.9.1/gems/rmagick-2.13.2/ext/RMagick/gem_make.out
  </code></pre>
  
  <p>After following suggestions, now I am getting this output:</p>
  
  <pre><code>Building native extensions.  This could take a while...
  ERROR:  Error installing rmagick:
      ERROR: Failed to build gem native extension.
  
          /usr/local/bin/ruby 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
  checking for HDRI disabled version of ImageMagick... yes
  checking for stdint.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=/usr/local/bin/ruby
  /usr/local/lib/ruby/1.9.1/mkmf.rb:381:in `try_do': The compiler failed to generate an executable file. (RuntimeError)
  You have to install development tools first.
      from /usr/local/lib/ruby/1.9.1/mkmf.rb:506:in `try_cpp'
      from /usr/local/lib/ruby/1.9.1/mkmf.rb:931:in `block in have_header'
      from /usr/local/lib/ruby/1.9.1/mkmf.rb:790:in `block in checking_for'
      from /usr/local/lib/ruby/1.9.1/mkmf.rb:284:in `block (2 levels) in postpone'
      from /usr/local/lib/ruby/1.9.1/mkmf.rb:254:in `open'
      from /usr/local/lib/ruby/1.9.1/mkmf.rb:284:in `block in postpone'
      from /usr/local/lib/ruby/1.9.1/mkmf.rb:254:in `open'
      from /usr/local/lib/ruby/1.9.1/mkmf.rb:280:in `postpone'
      from /usr/local/lib/ruby/1.9.1/mkmf.rb:789:in `checking_for'
      from /usr/local/lib/ruby/1.9.1/mkmf.rb:930:in `have_header'
      from extconf.rb:194:in `&lt;main&gt;'
  
  
  Gem files will remain installed in /usr/local/lib/ruby/gems/1.9.1/gems/rmagick-2.13.2 for inspection.
  Results logged to /usr/local/lib/ruby/gems/1.9.1/gems/rmagick-2.13.2/ext/RMagick/gem_make.out
  </code></pre>
  
  <p>Output Of mkmf.log:</p>
  
  <pre><code>checking for HDRI disabled version of ImageMagick... -------------------- yes
  
  --------------------
  
  "gcc -o conftest -I/usr/local/include/ruby-1.9.1/x86_64-linux -I/usr/local/include/ruby-1.9.1/ruby/backward -I/usr/local/include/ruby-1.9.1 -I.  -fopenmp -DMAGICKCORE_HDRI_ENABLE=0 -DMAGICKCORE_QUANTUM_DEPTH=16 -I/usr/include/ImageMagick-6    -fopenmp -DMAGICKCORE_HDRI_ENABLE=0 -DMAGICKCORE_QUANTUM_DEPTH=16 -I/usr/include/ImageMagick-6   conftest.c  -L. -L/usr/local/lib -Wl,-R/usr/local/lib  -L/usr/lib -lMagickCore-6.Q16      -L/usr/lib -lMagickCore-6.Q16    -Wl,-R -Wl,/usr/local/lib -L/usr/local/lib -lruby-static  -lpthread -lrt -ldl -lcrypt -lm   -lc"
  /usr/bin/ld: skipping incompatible /usr/lib/libMagickCore-6.Q16.so when searching for -lMagickCore-6.Q16
  /usr/bin/ld: skipping incompatible /usr/lib/libMagickCore-6.Q16.so when searching for -lMagickCore-6.Q16
  /usr/bin/ld: skipping incompatible /usr/lib/libMagickCore-6.Q16.so when searching for -lMagickCore-6.Q16
  /usr/bin/ld: cannot find -lMagickCore-6.Q16
  collect2: ld returned 1 exit status
  checked program was:
  /* begin */
  1: #include "ruby.h"
  </code></pre>
  
  <p>Output of  gem_make.out is same as the terminal output above.</p>