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 in recent uClibc
(>0.9.33), but available in older version of uClibc (<=0.9.33) whith a
different prototype than glibc.

dlinfo used by liblttng-ust-dl require RTLD_DI_LINKMAP that is not
available in uClibc.

To be able to use LTTng UST with uClibc, we need to disable the Dynamic
Linker Tracing functionality [2] if RTLD_DI_LINKMAP is not detected.

[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>