sanity: Verify that user isn't building in PSEUDO_IGNORE_PATHS

If a user builds in a path in PSEUDO_IGNORE_PATHS, random failures
are generated. Hence this patch adds a sanity check in sanity.bbclass
to ensure that a user isn't building in PSEUDO_IGNORE_PATHS.

[YOCTO #14179]

Signed-off-by: Dorinda Bassey <dorindabassey@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
(cherry picked from commit 7a681525)
Signed-off-by: Steve Sakoman <steve@sakoman.com>