optional/capi: use LIBRUBYARG_SHARED
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@58733 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
optional/capi: use LIBRUBYARG_SHARED
use LIBRUBYARG_SHARED for LDSHARED.
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@58733 b2dd03c8-39d4-4d8f-98ff-823fe69b080e