package/gcc: hide versions too old for the current arch

package/gcc: hide versions too old for the current arch

Begin the conversion from hard-coded dependencies on architectures, to
architecture-specified version requirement, using the newly introduced
BR2_ARCH_NEEDS_GCC_AT_LEAST_XXX symbols.

Hard-coded dependencies will be removed progressively, as archs are
individually converted over to using the new symbols.

We do not change the architecture-specific versions for ARC and
OpenRISC, because there is no point in doing so for those, as they use
special, non-upstream versions anyway.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Cc: Arnout Vandecappelle <arnout@mind.be>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>