Add test for restoring error_reporting on fatal error during silencing

This guard against the issue that GH-6904 would introduce when
run under --repeat 2 mode.

Author: nikic

Zend/tests/restore_error_reporting.phpt

@@ -0,0 +1,14 @@
+--TEST--
+Test error_reporting being restored after fatal error during silencing
+--FILE--
+<?php
+
+var_dump($undef_var);
+@eval('class self {}');
+
+?>
+--EXPECTF--
+Warning: Undefined variable $undef_var in %s on line %d
+NULL
+
+Fatal error: Cannot use 'self' as class name as it is reserved in %s on line %d