title: Error installed 'wdm' gem on Windows system
body: <p>I have a fresh install of Ruby 2.2.1 (32-bit) on my Windows 7 system.  I also installed the devkit without any reported errors.  Naturally I thought I could just install the 'wdm' gem with:</p>
  
  <pre><code>gem install wdm
  </code></pre>
  
  <p>However, it errors out.  The entire output is a bit much to post the entire thing so truncated the following points come up.</p>
  
  <pre><code>C:/Ruby22/bin/ruby.exe -r ./siteconf20150318-1712-oq5nlb.rb extconf.rb
  checking for main() in -lkernel32... yes
  checking for windows.h... yes
  checking for ruby.h... yes
  checking for HAVE_RUBY_ENCODING_H... yes
  creating Makefile
  
  make "DESTDIR=" clean
  
  make "DESTDIR="
  generating wdm_ext-i386-mingw32.def
  compiling entry.c
  In file included from entry.c:1:0:
  wdm.h:3:0: warning: "WINVER" redefined [enabled by default]
  ...
  wdm.h:4:0: warning: "_WIN32_WINNT" redefined [enabled by default]
  ...
  warning: #warning Please include winsock2.h before windows.h [-Wcpp]
  compiling monitor.c  (this is repeated for multiple *.c files)
  ...
  rb_monitor.o: In function `rb_monitor_run_bang':
  C:\Ruby22\lib\ruby\gems\2.2.0\gems\wdm-0.1.0\ext\wdm/rb_monitor.c:508: undefined reference to `rb_thread_blocking_region'
  collect2.exe: error: ld returned 1 exit status
  make: *** [wdm_ext.so] Error 1
  
  make failed, exit code 2
  </code></pre>
  
  <p>Did I miss something?</p>