Disable gcc-4.8.x + binutils-2.25 + MIPS combination

This combination causes a compilation failure of the host-gcc-final
recipe like this one:

/br/output/host/usr/mips-buildroot-linux-gnu/bin/ld:
.libs/gload.o: relocation R_MIPS_HI16 against `__gnu_local_gp' can not
be used when making a shared object; recompile with -fPIC

The problem is the file 'libatomic/gload.c' is compiled without -fPIC
when using binutils-2.25. All gcc (with libatomic) versions below 4.9.3
are affected by this issue.

Here is a summary of affected/unaffected versions in Buildroot:

4.7.x: unaffected (doesn't have libatomic)
4.8.x: affected
4.9.x: unaffected (we have 4.9.3 which is fixed)
5.1.x: unaffected

The fix can be found here:

  https://github.com/gcc-mirror/gcc/commit/57f5c0954f95cb37f995d60167ddde06c7d6e697



However, given the following reasons...

- Upstream gcc 4.8 branch is closed.
- The fix is very hard to backport from 4.9 to 4.8.
- This stuff is insanely sensitive and not working at all could be
  better than looking like it works but not quite.

...I think the best choice is to disable that combination in Buildroot.

Signed-off-by: Vicente Olivert Riera <Vincent.Riera@imgtec.com>
Reviewed-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>