* configure.in (install-static-library): add option to enable/
  disable to install static ruby library.  defaulted to "no" if
  enable-shared.  [Feature #12845]
* tool/rbinstall.rb (local-arch-lib): respect the option.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@56434 b2dd03c8-39d4-4d8f-98ff-823fe69b080e