Merges a patch form naclports.

* configure.in (RUBY_NACL and others): Supports PNaCl.
* dln.c: replace the old hacky dynamic loading over HTTP with nacl_io.
* file.c: tenatively use access(2) instead of eaccess.
  (rb_file_load_ok): weaken with attribute but not by postprocess.
* io.c (socket.h): now NaCl has socket.h
  (flock): disable here instead of nacl/ioctl.h
* nacl/GNUmakefile.in (CC, LD, NM, AR, AS, RANLIB, OBJDUMP, OBJCOPY):
  respect path to them if they are absolute.
  This helps naclports to build ruby in their source tree.
  (PROGRAM_NMF, .SUFFIXES): support .pnexe for PNaCl.
  (ruby.o, file.o): move the hack to attributes in ruby.c and file.c
* nacl/ioctl.h: removed. move the hack to io.c.
* nacl/nacl-config.rb: support arm, pnacl and others.
* nacl/pepper_main.c: support build in a naclports tree.
* ruby.c (rb_load_file): weaken with attribute but not by postprocess.

The patch is by sbc@google.com and the Native Client Authors.
It is available at:
* https://chromium.googlesource.com/external/naclports.git/+/873ca4910a5f9d4206306aacb4ed79c587c6a5f3/ports/ruby/nacl.patch

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@47872 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
Allow failure of sighandler installation on NativeClient.

* signal.c (install_signalhandler, init_sigchld): allow failure because it
  always fails with ENOSYS on NaCl.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@47873 b2dd03c8-39d4-4d8f-98ff-823fe69b080e