title: Fixing /usr/local/include/string.h on Mac
body: <p>I can no longer compile any C or ruby code, as I have messed up /usr/local/include. </p>
  
  <p>This is the error I get when doing anything involving C, including making a new rails application. </p>
  
  <p>I am certain I have done something with /usr/local/include when I was playing around with C. </p>
  
  <p>I've reinstalled everything a number of times, including XCode and Command Line Tools. </p>
  
  <p>Does anyone have any suggestions? Would be much appreciated!</p>
  
  <pre><code>*Fetching gem metadata from https://rubygems.org/...........
  Fetching version metadata from https://rubygems.org/...
  Fetching dependency metadata from https://rubygems.org/..
  Resolving dependencies....
  Using rake 11.0.1
  Using i18n 0.7.0
  Installing json 1.8.3 with native extensions
  
  Gem::Installer::ExtensionBuildError: ERROR: Failed to build gem native extension.
  
      /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/bin/ruby extconf.rb
  creating Makefile
  
  make "DESTDIR="
  compiling generator.c
  In file included from generator.c:1:
  In file included from ./../fbuffer/fbuffer.h:5:
  In file included from /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/include/ruby-2.0.0/ruby.h:33:
  In file included from /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/include/ruby-2.0.0/ruby/ruby.h:51:
  /usr/local/include/string.h:44:1: error: unknown type name '__BEGIN_NAMESPACE_STD'
  __BEGIN_NAMESPACE_STD
  ^
  /usr/local/include/string.h:46:1: error: expected identifier or '('
  extern void *memcpy (void *__restrict __dest, const void *__restrict __src,
  ^
  /usr/local/include/string.h:51:6: error: expected function body after function declarator
       __THROW __nonnull ((1, 2));
       ^*
  </code></pre>