socket (rsock_connect): fix and refactor for blocking

* ext/socket/init.c (rsock_connect): refactor for blocking
  (wait_connectable): clear error before wait
  [Bug #9356]

We no longer use non-blocking sockets to emulate blocking behavior,
so eliminate error-prone and confusing platform-dependent code.
According to POSIX, connect() only needs to be called once in the
face of EINTR, so do not loop on it.

Before waiting on connect, drop any pending errors, since
rb_wait_for_single_fd may not clear the existing error
properly.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@47617 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
* 2014-09-18

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@47618 b2dd03c8-39d4-4d8f-98ff-823fe69b080e