buildroot

package/glibc: needs kernel headers >= 3.10 on powerpc64le

Since glibc 2.26, kernel headers >= 3.10 are needed on powerpc64le [1].
In order to prepare the glibc bump to this version, we don't allow to
build a Buildroot toolchain with kernel headers older than 3.10.

[1] https://sourceware.org/git/?p=glibc.git;a=commit;h=c2ff5ec13fca1bdd1cd646a0260808386d7bd7ff

Signed-off-by: Romain Naour <romain.naour@gmail.com>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Cc: "Yann E. MORIN" <yann.morin.1998@free.fr>
Reviewed-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>