title: can't install gems with Bundler
body: <p>Im trying to install <a href="http://wpscan.org/" rel="nofollow">wpscan</a> 
  I have macbook pro 10.9.2
  Im running mavericks osx. </p>
  
  <p>I followed the instruction:</p>
  
  <pre><code>git clone https://github.com/wpscanteam/wpscan.git
  cd wpscan
  </code></pre>
  
  <p>and then I'm trying to </p>
  
  <pre><code>sudo gem install bundler &amp;&amp; bundle install --without test development
  </code></pre>
  
  <p>and after that I get this error: </p>
  
  <p>sudo gem install bundler &amp;&amp; bundle install --without test development</p>
  
  <pre><code>Successfully installed bundler-1.6.1
  Parsing documentation for bundler-1.6.1
  1 gem installed
  Fetching gem metadata from https://rubygems.org/.........
  Fetching additional metadata from https://rubygems.org/..
  Resolving dependencies...
  
  Gem::Installer::ExtensionBuildError: ERROR: Failed to build gem native extension.
  
      /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/bin/ruby extconf.rb 
  checking for ffi.h... no
  checking for ffi.h in /usr/local/include,/usr/include/ffi... yes
  checking for ffi_call() in -lffi... yes
  checking for ffi_prep_closure()... yes
  checking for ffi_raw_call()... no
  checking for rb_thread_blocking_region()... yes
  checking for rb_thread_call_with_gvl()... yes
  checking for rb_thread_call_without_gvl()... yes
  checking for ffi_prep_cif_var()... no
  creating extconf.h
  creating Makefile
  
  make "DESTDIR="
  compiling AbstractMemory.c
  compiling ArrayType.c
  compiling Buffer.c
  compiling Call.c
  Call.c:303:5: warning: implicit declaration of function 'rb_thread_call_without_gvl' is invalid in C99 [-Wimplicit-function-declaration]
      rbffi_thread_blocking_region(call_blocking_function, data, (void *) -1, NULL);
      ^
  ./Thread.h:78:39: note: expanded from macro 'rbffi_thread_blocking_region'
  # define rbffi_thread_blocking_region rb_thread_call_without_gvl
                                        ^
  1 warning generated.
  compiling ClosurePool.c
  compiling DataConverter.c
  DataConverter.c:43:1: warning: control may reach end of non-void function [-Wreturn-type]
  }
  ^
  1 warning generated.
  compiling DynamicLibrary.c
  compiling ffi.c
  compiling Function.c
  Function.c:479:33: warning: incompatible pointer types passing 'VALUE (void *)' to parameter of type 'void *(*)(void *)' [-Wincompatible-pointer-types]
          rb_thread_call_with_gvl(callback_with_gvl, &amp;cb);
                                  ^~~~~~~~~~~~~~~~~
  Function.c:102:46: note: passing argument to parameter 'func' here
  extern void *rb_thread_call_with_gvl(void *(*func)(void *), void *data1);
                                               ^
  Function.c:563:9: warning: implicit declaration of function 'rb_thread_call_without_gvl' is invalid in C99 [-Wimplicit-function-declaration]
          rb_thread_call_without_gvl(async_cb_wait, &amp;w, async_cb_stop, &amp;w);
          ^
  Function.c:738:1: warning: control reaches end of non-void function [-Wreturn-type]
  }
  ^
  3 warnings generated.
  compiling FunctionInfo.c
  compiling LastError.c
  compiling LongDouble.c
  compiling MappedType.c
  compiling MemoryPointer.c
  compiling MethodHandle.c
  compiling Platform.c
  compiling Pointer.c
  compiling Struct.c
  compiling StructByReference.c
  compiling StructByValue.c
  compiling StructLayout.c
  compiling Thread.c
  compiling Type.c
  compiling Types.c
  compiling Variadic.c
  linking shared-object ffi_c.bundle
  clang: error: unknown argument: '-multiply_definedsuppress' [-Wunused-command-line-argument-hard-error-in-future]
  clang: note: this will be a hard error (cannot be downgraded to a warning) in the future
  make: *** [ffi_c.bundle] Error 1
  
  
  Gem files will remain installed in /var/folders/pf/hl1jk3kx5_j2q70fbwyj18180000gn/T/bundler20140407-7061-7v0bbm/ffi-1.9.3/gems/ffi-1.9.3 for inspection.
  Results logged to /var/folders/pf/hl1jk3kx5_j2q70fbwyj18180000gn/T/bundler20140407-7061-7v0bbm/ffi-1.9.3/gems/ffi-1.9.3/ext/ffi_c/gem_make.out
  An error occurred while installing ffi (1.9.3), and Bundler cannot continue.
  Make sure that `gem install ffi -v '1.9.3'` succeeds before bundling.
  </code></pre>
  
  <p>can anyone help me? 
  Thanks.</p>