95448347 made lix require libatomic if the platform is able to link a
simple program using atomics, but it should actually be the other way
around. We need to require libatomic if it fails.
Change-Id: I6a6a6964ca6ee90a59314ddf1865753e83713772
Some platforms like 32-Bit PowerPC need linking against libatomic.
Try to compile and link a very simple snippet of code which uses atomics
and make libatomic required if it fails.
Because we're using `dependency('atomic')`, the required meson versions
gets bumped to 1.7.0. See https://mesonbuild.com/Dependencies.html#atomic-stdatomic
Change-Id: I6a6a696471e1d352fb161c537ba9023b97c2d31e
Marie Ramlow