[PATCH] lib/util: Fix build for lttng libraries that does not support tracef

[Ralph Böhme]

On Tue, Sep 12, 2017 at 08:02:28PM +0000, Christof Schmitt via samba-technical wrote:
> On a system that has older lttng-ust development headers installed that
> do not yet provide the tracef api, configure fails with:
> 
> Checking for library lttng-ust : yes
> ERROR: Target 'lttng-ust' in directory /samba/lib/util re-defined as EMPTY - was SYSLIB
> 
> Fix the initialization order in waf, to not redefine the lttng-ust
> target

lgtm&pushed.

Cheerio!
-slow