Added new config symbol `HARDEN_BRANCH_HISTORY` in order to harden
Spectre style attacks against branch history and fixed rejects in
following patches:
* generic/hack-4.14/220-gc_sections.patch
* generic/backport-4.14/306-v4.16-netfilter-remove-saveroute-indirection-in-struct-nf_.patch
Other patches refreshed automagically.
Run tested on ipq40xx/glinet-b1300 and mvebu/turris-omnia.
Signed-off-by: Petr Štetiar <ynezz@true.cz>
565159db57