[Artful/Xenial] Prevent linking perf command to libbfd

[Stefan Bader]

BugLink: https://bugs.launchpad.net/bugs/1748922

Impact: Linking perf (part of the linux-tools package) against libbfd
prevents users to have linux-tools of different kernel versions installed
in parallel. Which makes debugging hard.

Fix: As stated above this had been fixed before but upstream changes of
the kernel between 3.2 and 4.4 voided those fixes. Unfortunately without
causing build failures but causing libbfd to be used again. This has
already been fixed up in Bionic. The first of the two patches needs a
backport for Xenial to make up for a file rename. The second can be
picked into both releases.

Testcase: Extracting ./usr/lib/linux-tools-*/perf from the generated
linux-tools package and inspecting it with ldd. Old builds will have
a reference to libbfd, the test builds did no longer.

Risk of regression: low (change of build option which has been done before
and also for some time in Bionic).

-Stefan