If dwz is not available, then the libbacktrace test b3test_dwz_buildid fails
like this:
...
gmake[4]: *** No rule to make target 'b3test_dwz_buildid'
...

Fix this by guarding the test with HAVE_DWZ.

Tested on x86_64 with and without dwz installed.

2019-02-26  Tom de Vries  <tdevries@suse.de>

	* Makefile.am (TESTS): Only add b3test_dwz_buildid if HAVE_DWZ.
	* Makefile.in: Regenerate.

From-SVN: r269204