lttng-tools: disable on uClibc/musl

lttng-tools: disable on uClibc/musl

lttng-tools has been broken on uClibc/musl since a long time due to
dlmopen() and LM_ID_BASE not being implemented. The issue has been
reported to the upstream lttng developers more than two months ago [1],
and no fix has been provided. Therefore, it's time to disable it on
uClibc and musl.

Fixes:

  http://autobuild.buildroot.net/results/f9e82a87618bcdcd46d670697b5ac75836f7250d/
  (uclibc)

  http://autobuild.buildroot.net/results/cb0952483b580b053a585760e59d78d11f46fc60/
  (musl)

[1] https://lists.lttng.org/pipermail/lttng-dev/2017-February/026921.html

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>