Check for return value of `numa_available()`

[alessandropellegrini]

libnuma might be installed as well on non-NUMA architectures. In that scenario, issuing calls to NUMA API might produce undefined behaviour.

We should insert a small test in configure.ac which runs a simple program whose return value is that of numa_available(). In this way, we can ask the library to give us real information of NUMA facilities on a machine, despite the actual presence of the library.