Use LD_LIBRARY_PATH to find the build tree artifacts

The libtool wrapper scripts of the test binaries set LD_LIBRARY_PATH to
find the libknet library and its modules in the build tree, but RPATH
overrides this setting.  This is why RPATH is deprecated, so we switch
to RUNPATH instead by using --enable-new-dtags, which is already the
linker default on Debian ustable for example.

libknet/Makefile.am

@@ -86,6 +86,7 @@ EXTRA_libknet_la_DEPENDENCIES	= $(SYMFILE)
 libknet_la_LDFLAGS	= -Wl,--version-script=$(srcdir)/$(SYMFILE) \
 			  --export-dynamic \
 			  -Wl,-rpath=$(pkglibdir) \
+			  -Wl,--enable-new-dtags \
 			  -version-number $(libversion)
 
 libknet_la_LIBADD	= $(PTHREAD_LIBS) $(dl_LIBS) $(rt_LIBS) $(m_LIBS)