Fix AO_XSIZE_load/store definition order in generalize-small template

* src/atomic_ops/generalize-small.template (AO_XSIZE_load): Move
definition (which is based on AO_XSIZE_load_acquire) down to be after
AO_XSIZE_load_acquire definition.
* src/atomic_ops/generalize-small.template (AO_XSIZE_store): Move
definition (which is based on AO_XSIZE_store_release) down to be after
AO_XSIZE_store_release definition.
* src/atomic_ops/generalize-small.h : Regenerate.
Fix generalize-small template adding missed CAS-based fetch_and_add

* src/atomic_ops/generalize-small.template (AO_XSIZE_fetch_and_add):
Add missed definition based on CAS.
* src/atomic_ops/generalize-small.h: Regenerate.
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