Fix: disable liblttng-ust-dl if dlinfo is not available in C library

Fix: disable liblttng-ust-dl if dlinfo is not available in C library

According to uClibc commit [1], dlinfo is not available.
To be able to use LTTng UST with uClibc, we need to disable
the Dynamic Linker Tracing functionality [2].

[1] http://git.uclibc.org/uClibc/commit/?id=f3c9dc499c5c787ddd8c4320f2d44d2ae6e40c22
[2] http://lists.lttng.org/pipermail/lttng-dev/2014-February/022423.html

Signed-off-by: Romain Naour <romain.naour@openwide.fr>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>