package/numactl: make available on all architectures

Since its introduction in commit
b05e74ff in 2013, numactl has had an
explicit list of architectures that it supports. Interestingly, this
list does not include ARM, and now that rt-tests unconditionally needs
numactl, it meant the rt-tests package was no longer available on ARM.

Further investigation revealed that there is nothing in recent
versions of numactl that appears to be architecture-specific. It does
build with all of Buildroot toolchains currently used in the
autobuilders.

The only necessary changes are:

 * Exclude no-MMU architectures, as madvise() is used in the code
   base, and this is not available on no-MMU architectures.

 * Make sure to use -latomic when needed, as some atomic operations
   are used.

 * Backport a patch that fixes the .symver usage, which only affects
   really old gcc versions: only the old ARM Sourcery toolchain was
   affected by this. Newer gcc versions support the gcc "symver"
   attribute, so that the code that directly emits the assembly
   .symver directive is not invoked.

With these changes, numactl builds successfully on all our supported
toolchains.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>