[SRU Xenial/unstable] LP#1248289 -- Missing libunwind support in perf

[Andy Whitcroft]

It seems the patch applied in the current SRU round is insufficient to
fix the issue at hand.  We also need libbpf to actually make any
sensible use of the libuwind.  Following this email is a patch to add
binutils-dev as a Build-Depends: to make this available.  The original
reporter has tested a perf built with this additional fix to confirm
this is sufficient to fix the bug properly.

NOTE: that the fix as applied is benign so does not need to be reverted
nor is a respin for this required.  If we do respin for any reason it
might be nice to include this however.

Proposing for SRU to Xenial.  Also needed in unstable.

-apw