Verify that the RegExp constructor fails when providing flags and a RegExp instance pattern without flags

[pvginkel]

The specs state that the RegExp constructor should fail when flags are provided with a pattern that is an instance of the RegExp object. However, there are tests in the ECMA 262 test suite that test that the constructor should succeed in this case, only when the pattern does not have flags itself. Google Chrome also doesn't pass these tests.

Suppression of these tests must be verified. The test262-ignore.json file contains references to this issue.