Add a test case of the error code reported when we take a SEGV on a
mapped but inaccessible area. We broke this recently.

Based on a test case from John Sperbeck <jsperbeck@google.com>.
Acked-by: NJohn Sperbeck <jsperbeck@google.com>
Signed-off-by: NMichael Ellerman <mpe@ellerman.id.au>