libtraceevent: Fix build with binutils 2.35

libtraceevent: Fix build with binutils 2.35

Forwarded: https://lore.kernel.org/linux-trace-devel/20200725010623.GA194964@decadent.org.uk/T/#u

In binutils 2.35, 'nm -D' changed to show symbol versions along with
symbol names, with the usual @@ separator.  When generating
libtraceevent-dynamic-list we need just the names, so strip off the
version suffix if present.

Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Cc: stable@vger.kernel.org
Gbp-Pq: Topic bugfix/all
Gbp-Pq: Name libtraceevent-fix-build-with-binutils-2.35.patch