libmpx is not supported any longer and infact has been removed
completely from gcc-9, see
1e42d5c637
(From OE-Core rev: 547174fc834273af67a2f7e50a3cf6c8e3b900f4)
Signed-off-by: Khem Raj <raj.khem@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>