title: Failure to install old mysql2 gem
body: <p>I am using Mac High Sierra. I am using Ruby 2.2.1 with RVM. I need to use mysql2 with this Ruby on Rails app. I do have mysql 5.7 installed. I do have xcode installed along with the command-line tools.</p>
  
  <p>I am simply trying to get this company app working on my local machine. I know that I am very close but I have one final error when I do bundle install I receive the following error when I get to the mysql2 gem:</p>
  
  <pre><code>Fetching mysql2 0.3.18
  Installing mysql2 0.3.18 with native extensions
  Gem::Ext::BuildError: ERROR: Failed to build gem native extension.
  
      current directory: /Users/ahayden/.rvm/gems/ruby-2.2.1/gems/mysql2-0.3.18/ext/mysql2
  /Users/ahayden/.rvm/rubies/ruby-2.2.1/bin/ruby -r ./siteconf20180710-52515-2hjll8.rb extconf.rb
  checking for ruby/thread.h... yes
  checking for rb_thread_call_without_gvl() in ruby/thread.h... yes
  checking for rb_thread_blocking_region()... no
  checking for rb_wait_for_single_fd()... yes
  checking for rb_hash_dup()... yes
  checking for rb_intern3()... yes
  -----
  Using mysql_config at /usr/local/bin/mysql_config
  -----
  checking for mysql.h... yes
  checking for errmsg.h... yes
  checking for mysqld_error.h... yes
  -----
  Don't know how to set rpath on your system, if MySQL libraries are not in path mysql2 may not load
  -----
  -----
  Setting libpath to /usr/local/Cellar/mysql-connector-c/6.1.11/lib
  -----
  creating Makefile
  
  current directory: /Users/ahayden/.rvm/gems/ruby-2.2.1/gems/mysql2-0.3.18/ext/mysql2
  make "DESTDIR=" clean
  
  current directory: /Users/ahayden/.rvm/gems/ruby-2.2.1/gems/mysql2-0.3.18/ext/mysql2
  make "DESTDIR="
  compiling infile.c
  compiling client.c
  client.c:359:33: warning: implicit conversion loses integer precision: 'long' to 'unsigned int' [-Wshorten-64-to-32]
          elapsed_time = end_time - start_time;
                       ~ ~~~~~~~~~^~~~~~~~~~~~
  client.c:1163:56: warning: implicit conversion loses integer precision: 'size_t' (aka 'unsigned long') to 'unsigned int' [-Wshorten-64-to-32]
    mysql2rb = mysql2_mysql_enc_name_to_rb(charset_name, charset_name_len);
               ~~~~~~~~~~~~~~~~~~~~~~~~~~~               ^~~~~~~~~~~~~~~~
  2 warnings generated.
  compiling mysql2_ext.c
  compiling result.c
  result.c:186:17: warning: comparison of integers of different signs: 'int' and 'unsigned long' [-Wsign-compare]
    for (i = 0; i &lt; (len - 1); i++) {
                ~ ^  ~~~~~~~
  1 warning generated.
  linking shared-object mysql2/mysql2.bundle
  ld: library not found for -l-lpthread
  clang: error: linker command failed with exit code 1 (use -v to see invocation)
  make: *** [mysql2.bundle] Error 1
  
  make failed, exit code 2
  
  Gem files will remain installed in /Users/ahayden/.rvm/gems/ruby-2.2.1/gems/mysql2-0.3.18 for inspection.
  Results logged to /Users/ahayden/.rvm/gems/ruby-2.2.1/extensions/x86_64-darwin-17/2.2.0/mysql2-0.3.18/gem_make.out
  
  An error occurred while installing mysql2 (0.3.18), and Bundler cannot continue.
  Make sure that `gem install mysql2 -v '0.3.18'` succeeds before bundling.
  
  In Gemfile:
    mysql2
  </code></pre>
  
  <p>I've tried just installing mysql2 without the specific gem version and it works, but it did not fix my problem.  It seems to boil down to the bottom of the traceback where it cannot find library <code>-l-lpthread</code>.  Please help, I've been trying to do this all day.</p>