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Describe the bug
I cannot install fluent-plugin-filter-parse-postfix on Centos 6.x (on Centos 7.x work fine)

To Reproduce
/usr/sbin/fluent-gem install fluent-plugin-filter-parse-postfix on Centos 6.x

Expected behavior
Install the fluent-plugin-filter-parse-postfix on Centos 6.x

Your Environment

• Fluentd or td-agent version: td-agent 3.8.0-0.el6
• Operating system: CentOS release 6.9 (Final)
• Kernel version: 2.6.32-573.7.1.el6.x86_64

Your Error Log
Building native extensions. This could take a while...
ERROR: Error installing fluent-plugin-filter-parse-postfix:
ERROR: Failed to build gem native extension.

current directory: /opt/td-agent/embedded/lib/ruby/gems/2.4.0/gems/postfix_status_line-0.2.8/ext

/opt/td-agent/embedded/bin/ruby -r ./siteconf20210114-11431-jqydai.rb extconf.rb
checking for openssl/sha.h... *** 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
--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=/opt/td-agent/embedded/bin/$(RUBY_BASE_NAME)
/opt/td-agent/embedded/lib/ruby/2.4.0/mkmf.rb:468:in try_do': The compiler failed to generate an executable file. (RuntimeError) You have to install development tools first. from /opt/td-agent/embedded/lib/ruby/2.4.0/mkmf.rb:599:in try_cpp'
from /opt/td-agent/embedded/lib/ruby/2.4.0/mkmf.rb:1107:in block in have_header' from /opt/td-agent/embedded/lib/ruby/2.4.0/mkmf.rb:957:in block in checking_for'
from /opt/td-agent/embedded/lib/ruby/2.4.0/mkmf.rb:351:in block (2 levels) in postpone' from /opt/td-agent/embedded/lib/ruby/2.4.0/mkmf.rb:321:in open'
from /opt/td-agent/embedded/lib/ruby/2.4.0/mkmf.rb:351:in block in postpone' from /opt/td-agent/embedded/lib/ruby/2.4.0/mkmf.rb:321:in open'
from /opt/td-agent/embedded/lib/ruby/2.4.0/mkmf.rb:347:in postpone' from /opt/td-agent/embedded/lib/ruby/2.4.0/mkmf.rb:956:in checking_for'
from /opt/td-agent/embedded/lib/ruby/2.4.0/mkmf.rb:1106:in have_header' from extconf.rb:3:in

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

/opt/td-agent/embedded/lib/ruby/gems/2.4.0/extensions/x86_64-linux/2.4.0/postfix_status_line-0.2.8/mkmf.log

extconf failed, exit code 1

Gem files will remain installed in /opt/td-agent/embedded/lib/ruby/gems/2.4.0/gems/postfix_status_line-0.2.8 for inspection.
Results logged to /opt/td-agent/embedded/lib/ruby/gems/2.4.0/extensions/x86_64-linux/2.4.0/postfix_status_line-0.2.8/gem_make.out

mkmf.log:
"gcc -o conftest -I/opt/td-agent/embedded/include/ruby-2.4.0/x86_64-linux -I/opt/td-agent/embedded/include/ruby-2.4.0/ruby/backward -I/opt/td-agent/embedded/include/ruby-2.4.0 -I. -I/opt/td-agent/embedded/include -O2 -D_FORTIFY_SOURCE=2 -fstack-protector -O3 -g -pipe -I/opt/td-agent/embedded/include -I/opt/td-agent/embedded/include -O2 -D_FORTIFY_SOURCE=2 -fstack-protector -O3 -g -pipe -fPIC conftest.c -L. -L/opt/td-agent/embedded/lib -Wl,-rpath,/opt/td-agent/embedded/lib -L/opt/td-agent/embedded/lib -Wl,-rpath,/opt/td-agent/embedded/lib -L. -Wl,-rpath,/opt/td-agent/embedded/lib -L/opt/td-agent/embedded/lib -fstack-protector -rdynamic -Wl,-export-dynamic -L/opt/td-agent/embedded/lib -Wl,-rpath,/opt/td-agent/embedded/lib -Wl,-rpath,/opt/td-agent/embedded/lib -L/opt/td-agent/embedded/lib -lruby -lpthread -lrt -ldl -lcrypt -lm -lc"
checked program was:
/* begin */
1: #include "ruby.h"
2:
3: int main(int argc, char *argv)
4: {
5: return 0;
6: }
/ end */