gem install pgすると以下のエラーが出ます。
実行しているのはEC2でOSはAmazon Linuxです。

$ gem install pg -v '0.20.0'
Building native extensions.  This could take a while...
ERROR:  Error installing pg:
    ERROR: Failed to build gem native extension.
current directory: /home/ec2-user/.rbenv/versions/2.4.1/lib/ruby/gems/2.4.0/gems/pg-0.20.0/ext
/home/ec2-user/.rbenv/versions/2.4.1/bin/ruby -r ./siteconf20180206-457-e5bx4w.rb extconf.rb
checking for pg_config... yes
Using config values from /usr/bin/pg_config
checking for libpq-fe.h... no
Can't find the 'libpq-fe.h header
*** 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=/home/ec2-user/.rbenv/versions/2.4.1/bin/$(RUBY_BASE_NAME)
    --with-pg
    --without-pg
    --enable-windows-cross
    --disable-windows-cross
    --with-pg-config
    --without-pg-config
    --with-pg_config
    --without-pg_config
    --with-pg-dir
    --without-pg-dir
    --with-pg-include
    --without-pg-include=${pg-dir}/include
    --with-pg-lib
    --without-pg-lib=${pg-dir}/lib

To see why this extension failed to compile, please check the mkmf.log which can be found here:

  /home/ec2-user/.rbenv/versions/2.4.1/lib/ruby/gems/2.4.0/extensions/x86_64-linux/2.4.0-static/pg-0.20.0/mkmf.log

extconf failed, exit code 1

Gem files will remain installed in /home/ec2-user/.rbenv/versions/2.4.1/lib/ruby/gems/2.4.0/gems/pg-0.20.0 for inspection.
Results logged to /home/ec2-user/.rbenv/versions/2.4.1/lib/ruby/gems/2.4.0/extensions/x86_64-linux/2.4.0-static/pg-0.20.0/gem_make.out

以下を実行しましたが、エラー内容は変わりませんでした。

$ sudo yum install postgresql-devel

また、psqlの設定ファイルは以下の通りです。

$ ls -l /usr/bin/pg*
lrwxrwxrwx 1 root root     35  2月  6 08:47 /usr/bin/pg_archivecleanup -> /etc/alternatives/pg_archivecleanup
lrwxrwxrwx 1 root root     45  2月  6 08:36 /usr/bin/pg_archivecleanup96 -> ../../usr/lib64/pgsql96/bin/pg_archivecleanup
lrwxrwxrwx 1 root root     31  2月  6 08:47 /usr/bin/pg_basebackup -> /etc/alternatives/pg_basebackup
lrwxrwxrwx 1 root root     41  2月  6 08:36 /usr/bin/pg_basebackup96 -> ../../usr/lib64/pgsql96/bin/pg_basebackup
lrwxrwxrwx 1 root root     27  2月  6 08:47 /usr/bin/pg_config -> /etc/alternatives/pg_config
lrwxrwxrwx 1 root root     37  2月  6 08:47 /usr/bin/pg_config92 -> ../../usr/lib64/pgsql92/bin/pg_config
lrwxrwxrwx 1 root root     37  2月  6 08:36 /usr/bin/pg_config96 -> ../../usr/lib64/pgsql96/bin/pg_config
lrwxrwxrwx 1 root root     32  2月  6 08:47 /usr/bin/pg_controldata -> /etc/alternatives/pg_controldata
lrwxrwxrwx 1 root root     42  2月  6 08:36 /usr/bin/pg_controldata96 -> ../../usr/lib64/pgsql96/bin/pg_controldata
lrwxrwxrwx 1 root root     24  2月  6 08:47 /usr/bin/pg_ctl -> /etc/alternatives/pg_ctl
lrwxrwxrwx 1 root root     34  2月  6 08:36 /usr/bin/pg_ctl96 -> ../../usr/lib64/pgsql96/bin/pg_ctl
lrwxrwxrwx 1 root root     25  2月  6 08:47 /usr/bin/pg_dump -> /etc/alternatives/pg_dump
lrwxrwxrwx 1 root root     35  2月  6 08:47 /usr/bin/pg_dump92 -> ../../usr/lib64/pgsql92/bin/pg_dump
lrwxrwxrwx 1 root root     35  2月  6 08:36 /usr/bin/pg_dump96 -> ../../usr/lib64/pgsql96/bin/pg_dump
lrwxrwxrwx 1 root root     28  2月  6 08:47 /usr/bin/pg_dumpall -> /etc/alternatives/pg_dumpall
lrwxrwxrwx 1 root root     38  2月  6 08:47 /usr/bin/pg_dumpall92 -> ../../usr/lib64/pgsql92/bin/pg_dumpall
lrwxrwxrwx 1 root root     38  2月  6 08:36 /usr/bin/pg_dumpall96 -> ../../usr/lib64/pgsql96/bin/pg_dumpall
lrwxrwxrwx 1 root root     28  2月  6 08:47 /usr/bin/pg_isready -> /etc/alternatives/pg_isready
lrwxrwxrwx 1 root root     38  2月  6 08:36 /usr/bin/pg_isready96 -> ../../usr/lib64/pgsql96/bin/pg_isready
lrwxrwxrwx 1 root root     32  2月  6 08:47 /usr/bin/pg_receivexlog -> /etc/alternatives/pg_receivexlog
lrwxrwxrwx 1 root root     42  2月  6 08:36 /usr/bin/pg_receivexlog96 -> ../../usr/lib64/pgsql96/bin/pg_receivexlog
lrwxrwxrwx 1 root root     32  2月  6 08:47 /usr/bin/pg_recvlogical -> /etc/alternatives/pg_recvlogical
lrwxrwxrwx 1 root root     42  2月  6 08:36 /usr/bin/pg_recvlogical96 -> ../../usr/lib64/pgsql96/bin/pg_recvlogical
lrwxrwxrwx 1 root root     30  2月  6 08:47 /usr/bin/pg_resetxlog -> /etc/alternatives/pg_resetxlog
lrwxrwxrwx 1 root root     40  2月  6 08:36 /usr/bin/pg_resetxlog96 -> ../../usr/lib64/pgsql96/bin/pg_resetxlog
lrwxrwxrwx 1 root root     28  2月  6 08:47 /usr/bin/pg_restore -> /etc/alternatives/pg_restore
lrwxrwxrwx 1 root root     38  2月  6 08:47 /usr/bin/pg_restore92 -> ../../usr/lib64/pgsql92/bin/pg_restore
lrwxrwxrwx 1 root root     38  2月  6 08:36 /usr/bin/pg_restore96 -> ../../usr/lib64/pgsql96/bin/pg_restore
lrwxrwxrwx 1 root root     27  2月  6 08:47 /usr/bin/pg_rewind -> /etc/alternatives/pg_rewind
lrwxrwxrwx 1 root root     37  2月  6 08:36 /usr/bin/pg_rewind96 -> ../../usr/lib64/pgsql96/bin/pg_rewind
lrwxrwxrwx 1 root root     28  2月  6 08:47 /usr/bin/pg_standby -> /etc/alternatives/pg_standby
lrwxrwxrwx 1 root root     38  2月  6 08:36 /usr/bin/pg_standby96 -> ../../usr/lib64/pgsql96/bin/pg_standby
lrwxrwxrwx 1 root root     31  2月  6 08:47 /usr/bin/pg_test_fsync -> /etc/alternatives/pg_test_fsync
lrwxrwxrwx 1 root root     41  2月  6 08:36 /usr/bin/pg_test_fsync96 -> ../../usr/lib64/pgsql96/bin/pg_test_fsync
lrwxrwxrwx 1 root root     32  2月  6 08:47 /usr/bin/pg_test_timing -> /etc/alternatives/pg_test_timing
lrwxrwxrwx 1 root root     42  2月  6 08:36 /usr/bin/pg_test_timing96 -> ../../usr/lib64/pgsql96/bin/pg_test_timing
lrwxrwxrwx 1 root root     29  2月  6 08:47 /usr/bin/pg_xlogdump -> /etc/alternatives/pg_xlogdump
lrwxrwxrwx 1 root root     39  2月  6 08:36 /usr/bin/pg_xlogdump96 -> ../../usr/lib64/pgsql96/bin/pg_xlogdump
-rwxr-xr-x 1 root root 375360 10月 14  2012 /usr/bin/pgawk
lrwxrwxrwx 1 root root     25  2月  6 08:47 /usr/bin/pgbench -> /etc/alternatives/pgbench
lrwxrwxrwx 1 root root     35  2月  6 08:36 /usr/bin/pgbench96 -> ../../usr/lib64/pgsql96/bin/pgbench
-rwxr-xr-x 2 root root  15872  3月 17  2015 /usr/bin/pgrep

libpqを含むファイルがなかったのでこれが原因なのではないかと思い、以下を実行しましたがインストールできませんでした。

$ sudo yum install libpq-dev
読み込んだプラグイン:priorities, update-motd, upgrade-helper
amzn-main                                                                                           | 2.1 kB  00:00:00     
amzn-updates                                                                                        | 2.5 kB  00:00:00     
23 packages excluded due to repository priority protections
パッケージ libpq-dev は利用できません。

libpq-devがないためgem install pgでエラーが起きるのでしょうか?
上記が理由の場合どのようなコマンドでインストールできるでしょうか?
gem install pgのエラーを解決したいです。

恐れ入りますが、よろしくお願いいたします。