title: Why did gem install bson_ext fail on Windows?
body: <p>I got this error when I install bson_ext on Windows.</p>
  
  <p>The error message is:</p>
  
  <pre class="lang-none prettyprint-override"><code>Temporarily enhancing PATH to include DevKit...
  Building native extensions.  This could take a while...
  ERROR:  Error installing bson_ext:
      ERROR: Failed to build gem native extension.
  
  C:/Ruby193/bin/ruby.exe extconf.rb
  checking for asprintf()... no
  checking for ruby/st.h... yes
  checking for ruby/regex.h... yes
  checking for ruby/encoding.h... yes
  creating Makefile
  
  make "DESTDIR="
  generating cbson-i386-mingw32.def
  compiling bson_buffer.c
  compiling cbson.c
  cbson.c:150:15: warning: extra tokens at end of #ifdef directive
  cbson.c: In function 'pack_extra':
  cbson.c:201:27: warning: cast from pointer to integer of different size
  cbson.c: In function 'write_element':
  cbson.c:211:28: warning: cast to pointer from integer of different size
  cbson.c:317:17: warning: implicit declaration of function '_scprintf'
  compiling encoding_helpers.c
  linking shared-object bson_ext/cbson.so
  c:/devkit/mingw/bin/../lib/gcc/mingw32/4.5.2/../../../../mingw32/bin/ld.exe: cannot find -lmsvcrt-ru
  by191
  collect2: ld returned 1 exit status
  make: *** [cbson.so] Error 1
  
  
  Gem files will remain installed in C:/Ruby193/lib/ruby/gems/1.9.1/gems/bson_ext-1.9.1     for inspection.
  Results logged to C:/Ruby193/lib/ruby/gems/1.9.1/gems/bson_ext1.9.1/ext/cbson/gem_make.out
  </code></pre>
  
  <p>Can anybody help me?</p>