commit eab4aba3f5e06ea8f124d3e5ff6b3fa88c4807cd
Author: Mamoru TASAKA <mtasaka@fedoraproject.org>
Date:   Thu Dec 1 12:23:05 2022 +0900

    extconf.rb: use Rbconfig::CONFIG instead of mkmf CONFIG
    
    In mkmf.rb CONFIG is defined as CONFIG is defined as RbConfig::MAKEFILE_CONFIG
    and RbConfig::MAKEFILE_CONFIG is almost same as RbConfig::CONFIG
    except that RbConfig::MAKEFILE_CONFIG uses reference for other variables.
    
    Using CONFIG in extconf.rb causes error with ruby3.2 because now
    CONFIG['host_os'] uses reference for target_os variable, and extconf.rb
    expects that this variable is all expanded. So instead, use RbConfig::CONFIG .
    
    Closes #30

diff --git a/extconf.rb b/extconf.rb
index d17f926..55dcff5 100644
--- a/extconf.rb
+++ b/extconf.rb
@@ -14,7 +14,7 @@ $CFLAGS = case RUBY_VERSION
           else; ''
           end
 
-implementation = case CONFIG['host_os']
+implementation = case RbConfig::CONFIG['host_os']
                  when /linux/i; 'shadow'
                  when /sunos|solaris/i; 'shadow'
                  when /freebsd|mirbsd|netbsd|openbsd/i; 'pwd'