Fix failures on btest for NativeClient.
* bootstraptest/runner.rb (nacl?): New method to distinguish NaCl
  corss build.

* bootstraptest/test_io.rb: Skip unsupported operations.

* bootstraptest/test_literal.rb: ditto.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@38686 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
revert r38686 -- duplicate ChangeLog entry

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@38687 b2dd03c8-39d4-4d8f-98ff-823fe69b080e