meson: sort existing compiler tests

meson: sort existing compiler tests

The next patches will add more compiler tests.  Sort and group the
existing tests, keeping similar cc.has_* tests together and sorting them
alphabetically by macro name.  This should make it easier to look for
examples when adding new tests to meson.build.

Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>