Fix return type of AO_char/short/int_load_read() in read_ordered.h

* src/atomic_ops/sysdeps/read_ordered.h (AO_char_load_read,
AO_short_load_read, AO_int_load_read): Change return type (and the
type of "result" local variable) from AO_t to the type matching the
name of the function (i.e., unsigned char/short/int, respectively).
Move definitions of ordered loads/stores to inner separate headers
(code refactoring)

* src/Makefile.am (nobase_private_HEADERS): Add ordered_loads_only.h,
ordered_stores_only.h entries.
* src/atomic_ops/sysdeps/loadstore/ordered_loads_only.h: New file.
* src/atomic_ops/sysdeps/loadstore/ordered_stores_only.h: Likewise.
* src/atomic_ops/sysdeps/ordered_except_wr.h: Include
ordered_stores_only.h.
* src/atomic_ops/sysdeps/ordered_except_wr.h (AO_store_write,
AO_store_release, AO_char_store_write, AO_char_store_release,
AO_short_store_write, AO_short_store_release, AO_int_store_write,
AO_int_store_release): Move to ordered_stores_only.h (with the
corresponding AO_HAVE_x macros).
* src/atomic_ops/sysdeps/read_ordered.h: Include ordered_loads_only.h.
* src/atomic_ops/sysdeps/read_ordered.h (AO_load_read,
AO_load_acquire, AO_char_load_read, AO_char_load_acquire,
AO_short_load_read, AO_short_load_acquire, AO_int_load_read,
AO_int_load_acquire): Move to ordered_loads_only.h (with the
corresponding AO_HAVE_x macros).
Generate ordered_loads/stores_only headers from templates
(code refactoring)

* src/Makefile.am (EXTRA_DIST): Add ordered_loads_only.template,
ordered_stores_only.template entries.
* src/Makefile.am (BUILT_SOURCES): Add ordered_loads_only.h,
ordered_stores_only.h entries (move from nobase_private_HEADERS).
* src/Makefile.am (atomic_ops/sysdeps/loadstore/ordered_loads_only.h,
atomic_ops/sysdeps/loadstore/ordered_stores_only.h): New rule (to
generate header from the corresponding template).
* src/atomic_ops/sysdeps/loadstore/ordered_loads_only.h: Regenerate
(from the corresponding template).
* src/atomic_ops/sysdeps/loadstore/ordered_stores_only.h: Likewise.
* src/atomic_ops/sysdeps/loadstore/ordered_loads_only.template: New
template header (code copied from the corresponding header of
"loadstore" folder and parameterized with XSIZE and XCTYPE).
* src/atomic_ops/sysdeps/loadstore/ordered_stores_only.template:
Likewise.