Patch by Google Inc. [ruby-core:45073].

* configure.in (RUBY_NACL): New M4 func to configure variables for
  NaCl.
  (RUBY_NACL_CHECK_PEPPER_TYPES): New M4 func to check the old names
  of Pepper interface types.
  (BTESTRUBY): New variable to specify which ruby should be run on
  "make btest". NaCl can run the built binary by sel_ldr, but it need
  rbconfig.rb. So this variable is distinguished from $MINIRUBY.
  
* thread_pthread.c: Disabled some features on NaCl.

* io.c: ditto.

* process.c: ditto.

* signal.c: ditto.

* file.c: ditto.

* missing/flock.c: ditto.

* nacl/pepper_main.c: An example implementation of Pepper application
  that embeds Ruby.

* nacl/example.html: An example of web page that uses the Pepper
  application.

* nacl/nacl-config.rb: Detects variants of NaCl SDK.

* nacl/GNUmakefile.in: Makefile template for NaCl specific build
  process.

* nacl/package.rb: script for packaging a NaCl-Ruby embedding
  application. 

* nacl/reate_nmf.rb: Wrapper script of create_nmf.py

* dln.c (dln_load): Added a hack to call on NaCl.

* util.c (ruby_getcwd): Path to the current directort is not available
  on NaCl.



git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@35672 b2dd03c8-39d4-4d8f-98ff-823fe69b080e