* configure.in: revert r42008. strcasecmp() uses the current locale.

* include/ruby/ruby.h: ditto.

* st.c (st_strcasecmp): ditto.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@42009 b2dd03c8-39d4-4d8f-98ff-823fe69b080e