build: fix building error when building without libvirtd

build: fix building error when building without libvirtd

When building libvirt without libvirtd, we will receive the following error
message:

make[3]: Entering directory `/home/wency/rpmbuild/BUILD/libvirt-0.9.2/tools'
  CC     virsh-virsh.o
  CC     virsh-console.o
  GEN    virt-xml-validate
  GEN    virt-pki-validate
  CCLD   virsh
./src/.libs/libvirt.so: undefined reference to `numa_available'
./src/.libs/libvirt.so: undefined reference to `numa_max_node'
collect2: ld returned 1 exit status

The reason is that: we check numactl only when building qemu driver, and qemu
driver will not be built when bulding without libvirtd. So with_numactl's
value is check and we will not link libnuma.so.

In the other function, we call numa_available() and numa_max_node() only
when HAVE_NUMACTL is 1. We should do the same check in the function nodeGetMemoryStats().