【Ruby on Rails】railsでpgがインストールできないできない

postgreSQLをDBにしたrailsアプリケーションで

$ bundle install 

エラー文はこれ

An error occurred while installing pg (0.18.2), and Bundler cannot continue.
Make sure that `gem install pg -v '0.18.2'` succeeds before bundling.

とりあえず指示に従う。

$ gem install pg -v '0.18.2'

これもダメ

/System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/bin/ruby extconf.rb
checking for pg_config... yes
Using config values from /usr/local/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... no
checking for PQconnectdb() in -llibpq... no
checking for PQconnectdb() in -lms/libpq... no
Can't find the PostgreSQL client library (libpq)
*** extconf.rb failed ***
Could not create Makefile due to some reason, probably lack of necessary
libraries and/or headers.  Check the mkmf.log file for more details.  You may
need configuration options.

Provided configuration options:
--with-opt-dir
--without-opt-dir
--with-opt-include
--without-opt-include=${opt-dir}/include
--with-opt-lib
--without-opt-lib=${opt-dir}/lib
--with-make-prog
--without-make-prog
--srcdir=.
--curdir
--ruby=/System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/bin/ruby
--with-pg
--without-pg
--enable-windows-cross
--disable-windows-cross
--with-pg-config
--without-pg-config
--with-pg_config
--without-pg_config
--with-pg-dir
--without-pg-dir
--with-pg-include
--without-pg-include=${pg-dir}/include
--with-pg-lib
--without-pg-lib=${pg-dir}/
--with-pqlib
--without-pqlib
--with-libpqlib
--without-libpqlib
--with-ms/libpqlib
--without-ms/libpqlib

Gem files will remain installed in /Library/Ruby/Gems/2.0.0/gems/pg-0.18.2 for  inspection.
Results logged to /Library/Ruby/Gems/2.0.0/gems/pg-0.18.2/ext/gem_make.out

これでやっと通った。結論はこれ

 ARCHFLAGS="-arch x86_64" bundle install