configure.in: correctly tests dtrace -G in version 1.11

* configure.in (RUBY_DTRACE_POSTPROCESS): dtrace version SUN D 1.11
  introduces a check in the dtrace compiler to ensure that probes
  actually exist. If there are no probes, then the -G step will
  fail. As this test is only being used to determine whether -G is
  necessary (for instance, on OSX it is not), adding a real probe to
  the conftest allows it to succeed on newer versions of dtrace.
  Patch by Eric Saxby <sax AT livinginthepast.org> at
  [ruby-core:55826].  [Fix GH-351], [Bug #8606].

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@41815 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
configure.in: check exit statuses

* configure.in (RUBY_DTRACE_POSTPROCESS): check exit statuses of
  commands.  [Bug #8606]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@41816 b2dd03c8-39d4-4d8f-98ff-823fe69b080e