configure correctly tests dtrace -G in version 1.11

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 dtrace -G step will fail.

Without this fix, on operating systems with the newer version of dtrace (for instance SmartOS platform images newer than June 2013) the configure step fails with the following error:
dtrace: failed to link script conftest_provider: No probe sites found for declared provider

This makes configure incorrectly determine that -G is *not* needed, and make subsequently fails.

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.