Added xdebug_call phpt test

Summary: This diff adds the relevant xdebug phpt test for the xdebug_call_* functions.
There are actually two more tests related to these functions, but they
test an undocumented (and unimplemented in hhvm) feature- namely passing
a depth argument to each xdebug_call_* function. If this feature is added
later, those tests should be added.

Depends on D1388555

Reviewed By: @sgolemon

Differential Revision: D1388860