Any existing tests are going to be written under this assumption...

The default PHP executable was not set when no args were provided.

Closes GH-4894.

Otherwise we would try to access an array element of `false`, which
issues a notice as of PHP 7.4.0.  This would happen, for instance, for
bug63447_001.phpt if CGI is not available.

Commit 5649267[1] changed run-tests.php to only delete .post files for
passing tests.  However, that code wouldn't be exercised at all, since
`run_test()` already returned, so we move the deletion upwards.

[1]
<http://git.php.net/?p=php-src.git;a=commit;h=5649267b257c78e46a934434c0bff894e0b5b694>

These were being reported under the wrong name ... which means that
they don't show up as failures on azure :(

Due to a typo in commit e1151c9[1], succeeding XFAIL test without an
EXPECTF or EXPECTREGEX section have been reported reported as passed
instead of warned.

[1] <http://git.php.net/?p=php-src.git;a=commit;h=e1151c9549cf5a7235c1609019f79bbb1bbcdbea>

* PHP-7.3:
  Remove .post files only for passing tests

* PHP-7.2:
  Remove .post files only for passing tests

This allows the sh script for failing tests with --POST-- to work