Fix: liblttng-ust-ctl have dependencies on liburcu

Fix: liblttng-ust-ctl have dependencies on liburcu

Observed issue
==============

On a yocto build the liblttng-ust-ctl shared object have dependencies on
liburcu.

(The 'not found's are irrelevant here)
 ./liblttng-ust-ctl.so: /lib/x86_64-linux-gnu/libc.so.6: version `GLIBC_2.32' not found (required by ./liblttng-ust-ctl.so)
        linux-vdso.so.1 (0x00007ffc07910000)
        libpseudo.so => /root/oe-core/build/tmp-glibc/sysroots-components/x86_64/pseudo-native/usr/lib/pseudo/lib64/libpseudo.so (0x00007f8fa3e0d000)
        librt.so.1 => /lib/x86_64-linux-gnu/librt.so.1 (0x00007f8fa3c05000)
        libdl.so.2 => /lib/x86_64-linux-gnu/libdl.so.2 (0x00007f8fa3a01000)
        liburcu-bp.so.6 => not found
        liburcu-cds.so.6 => not found
        libpthread.so.0 => /lib/x86_64-linux-gnu/libpthread.so.0 (0x00007f8fa37e2000)
        libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007f8fa33f1000)
        /lib64/ld-linux-x86-64.so.2 (0x00007f8fa4069000)

On my ubuntu system:

	linux-vdso.so.1 (0x00007ffcd20aa000)
	librt.so.1 => /lib/x86_64-linux-gnu/librt.so.1 (0x00007faaf5282000)
	libdl.so.2 => /lib/x86_64-linux-gnu/libdl.so.2 (0x00007faaf527c000)
	libnuma.so.1 => /lib/x86_64-linux-gnu/libnuma.so.1 (0x00007faaf526f000)
	libpthread.so.0 => /lib/x86_64-linux-gnu/libpthread.so.0 (0x00007faaf524c000)
	libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007faaf505a000)
	/lib64/ld-linux-x86-64.so.2 (0x00007faaf52ed000)

Cause
=====

The default behavior for AC_CHECK_LIB, when the `action-if-found` is NOT
defined, is to prepend the library to LIBS. [1]

"
If action-if-found is not specified, the default action prepends
-llibrary to LIBS and defines ‘HAVE_LIBlibrary’ (in all capitals).
"

It is important to note that the LIBS variable is used for ALL linking.

This is normally not a problem for most distributions since they force
the use of `--as-needed` at the toolchain level (gcc specs) (for example
debian [2]). One could also pass the `--as-needed` flag manually but
libtool reorganize flags in the case of shared object creation [3].

In our case, we normally explicitly state the dependencies via the *_LIBADD
automake clause. We do not rely on the LIBS variable.

For the current tree, when the configure script is run, the LIBS
variable has the following value:

 LIBS='-lnuma -lurcu-bp -lurcu-bp -lurcu-cds -lpthread '

The current configure.ac does define what seems to be `empty but
defined` clause for the `action-if-found` as "[]". This is not a valid
"empty but defined" `action-if-find` clause and end up generating the
default behavior as defined in [1]. "[ ]" would be but is supposedly not
the case for all autoconf version.

This leads to unnecessary dependencies for most of the shared objects, at
link time, generated when using a distro that do not enforce the
`--as-needed` flag on linking.

Solution
========

Define an actual no-op shell operation `:` for the `action-if-found`
parameter.

For libnuma define HAVE_LIBNUMA manually. This prevent the prepending to
LIBS while providing the HAVE_LIB* default behavior.

Known drawbacks
=========

None.

References
==========
[1] https://www.gnu.org/software/autoconf/manual/autoconf-2.69/html_node/Libraries.html
[2] https://salsa.debian.org/toolchain-team/gcc/-/blob/master/debian/patches/gcc-as-needed.diff
[3] https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=347650

Signed-off-by: Jonathan Rajotte <jonathan.rajotte-julien@efficios.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Change-Id: I8fbb41eb85a98800902fbd23bfbea3ed41faaf26