toolchain: gcc bug 85180 is fixed in gcc >= 8.x

Gcc bug 85180 (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85180

) has
been fixed on Gcc version >= 8.x, so this commit adjusts the
BR2_TOOLCHAIN_HAS_GCC_BUG_85180 option to no longer be true when the
gcc version is >= 8.x.

Signed-off-by: Giulio Benetti <giulio.benetti@micronovasrl.com>
Reviewed-by: Petr Vorel <petr.vorel@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>