There's no need to specify an ancient GCC version here as Boost will
probe it.
(From OE-Core rev: 2339bf5b0aceb8e55f4b38e44b2383389e514393)
Signed-off-by: Ross Burton <ross.burton@arm.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>