title: Gem::Installer::ExtensionBuildError: ERROR: Failed to build gem native extension
body: <p>To provide some background - I've just downloaded a Git Repo from GitHub, for a friends app and I am attempting to launch it from my Mac ('rails s'). However, I am being hit with the following error // see below // when running 'bundle install'. It seems as if the 'pg' (postgreSQL) gem is having some sort of obscure installation error. Any help would be appreciated!</p>
  
  <h3>I have tried this command to no avail:</h3>
  
  <p>$gem install pg -- --with-pg-config= /usr/bin/pg_config/</p>
  
  <h3>And here is the error log:</h3>
  
  <pre><code>Installing pg (0.15.0) with native extensions 
  Gem::Installer::ExtensionBuildError: ERROR: Failed to build gem native extension.
  
          /usr/local/rvm/rubies/ruby-1.9.3-p194/bin/ruby extconf.rb 
  checking for pg_config... yes
  Using config values from /usr/bin/pg_config
  checking for libpq-fe.h... yes
  checking for libpq/libpq-fs.h... yes
  checking for pg_config_manual.h... yes
  checking for PQconnectdb() in -lpq... yes
  checking for PQconnectionUsedPassword()... yes
  checking for PQisthreadsafe()... yes
  checking for PQprepare()... yes
  checking for PQexecParams()... yes
  checking for PQescapeString()... yes
  checking for PQescapeStringConn()... yes
  checking for PQescapeLiteral()... yes
  checking for PQescapeIdentifier()... yes
  checking for PQgetCancel()... yes
  checking for lo_create()... yes
  checking for pg_encoding_to_char()... yes
  checking for pg_char_to_encoding()... yes
  checking for PQsetClientEncoding()... yes
  checking for PQlibVersion()... yes
  checking for PQping()... yes
  checking for PQsetSingleRowMode()... no
  checking for rb_encdb_alias()... yes
  checking for rb_enc_alias()... no
  checking for rb_thread_call_without_gvl()... yes
  checking for rb_thread_call_with_gvl()... yes
  checking for rb_thread_fd_select()... yes
  checking for rb_w32_wrap_io_handle()... no
  checking for PGRES_COPY_BOTH in libpq-fe.h... no
  checking for PGRES_SINGLE_TUPLE in libpq-fe.h... no
  checking for struct pgNotify.extra in libpq-fe.h... yes
  checking for unistd.h... yes
  checking for ruby/st.h... yes
  creating extconf.h
  creating Makefile
  
  make
  compiling gvl_wrappers.c
  compiling pg.c
  pg.c: In function ‘Init_pg_ext’:
  pg.c:384: error: ‘PQPING_OK’ undeclared (first use in this function)
  pg.c:384: error: (Each undeclared identifier is reported only once
  pg.c:384: error: for each function it appears in.)
  pg.c:386: error: ‘PQPING_REJECT’ undeclared (first use in this function)
  pg.c:388: error: ‘PQPING_NO_RESPONSE’ undeclared (first use in this function)
  pg.c:390: error: ‘PQPING_NO_ATTEMPT’ undeclared (first use in this function)
  make: *** [pg.o] Error 1
  
  
  Gem files will remain installed in /usr/local/rvm/gems/ruby-1.9.3-p194/gems/pg-0.15.0 for inspection.
  Results logged to /usr/local/rvm/gems/ruby-1.9.3-p194/gems/pg-0.15.0/ext/gem_make.out
  An error occured while installing pg (0.15.0), and Bundler cannot continue.
  Make sure that `gem install pg -v '0.15.0'` succeeds before bundling.
  </code></pre>
  
  <h3>GemFile</h3>
  
  <pre><code>source 'https://rubygems.org'
  
  gem 'rails', '3.2.11'
  
  # Bundle edge Rails instead:
  # gem 'rails', :git =&gt; 'git://github.com/rails/rails.git'
  
  gem 'pg'
  gem 'json'
  
  # Gems used only for assets and not required
  # in production environments by default.
  group :assets do
    gem 'sass-rails',   '~&gt; 3.2.3'
    gem 'coffee-rails', '~&gt; 3.2.1'
  
    # See https://github.com/sstephenson/execjs#readme for more supported runtimes
    # gem 'therubyracer', :platforms =&gt; :ruby
  
    gem 'uglifier', '&gt;= 1.0.3'
  end
  
  gem 'jquery-rails'
  
  gem 'devise'
  
  gem 'rails-backbone'
  
  gem 'nokogiri'
  # To use ActiveModel has_secure_password
  # gem 'bcrypt-ruby', '~&gt; 3.0.0'
  
  # To use Jbuilder templates for JSON
  # gem 'jbuilder'
  
  # Use unicorn as the app server
  # gem 'unicorn'
  
  # Deploy with Capistrano
  # gem 'capistrano'
  
  # To use debugger
  # gem 'ruby-debug'
  </code></pre>