[PATCH][SRU][XENIAL] ftrace/x86: Set ftrace_stub to weak to prevent gcc from using short jumps to it

[Thadeu Lima de Souza Cascardo]

This has been merged to master-next on Feb 13, as part of the v4.4.45
update.

Please, make sure the bug is in the right state for verification.
Ubuntu-4.4.0-67.88 should have it applied.

Thanks.
Cascardo.