title: Cannot install gem file
body: <p>I've been on this for a few hrs already googled everything. Tried tons of answers, im using ruby x64 and devkit x64 (originaly isntalled the incorect one x32 but i just deleted it and installed the correct one x64)
  Cant install json or (my actual target) ruby-debug-ide -v 0.4.32
  gem version = 2.4.7
  ruby version =ruby 2.4.2p198 (2017-09-14 revision 59899) [x64-mingw32]</p>
  
  <pre><code>C:\WINDOWS\system32&gt;gem install json
  Building native extensions.  This could take a while...
  ERROR:  Error installing json:
          ERROR: Failed to build gem native extension.
  
      C:/Ruby24-x64/bin/ruby.exe -r ./siteconf20171013-12212-1y42085.rb extconf.rb
  creating Makefile
  
  make "DESTDIR=" clean
  
  make "DESTDIR="
  generating generator-x64-mingw32.def
  compiling generator.c
  linking shared-object json/ext/generator.so
  c:/ruby24-x64/programing/mingw/bin/../lib/gcc/x86_64-w64-mingw32/4.7.2/../../../../x86_64-w64-mingw32/bin/ld.exe: cannot find -lgmp
  collect2.exe: error: ld returned 1 exit status
  make: *** [generator.so] Error 1
  
  make failed, exit code 2
  
  Gem files will remain installed in C:/Ruby24-x64/lib/ruby/gems/2.4.0/gems/json-2.1.0 for inspection.
  Results logged to C:/Ruby24-x64/lib/ruby/gems/2.4.0/extensions/x64-mingw32/2.4.0/json-2.1.0/gem_make.out
  </code></pre>