ada: Add __atomic_store_n binding to System.Atomic_Primitives
This is modeled on the existing binding for __atomic_load_n.
gcc/ada/
* libgnat/s-atopri.ads (Atomic_Store): New generic procedure.
(Atomic_Store_8): New instantiated procedure.
(Atomic_Store_16): Likewise.
(Atomic_Store_32): Likewise.
(Atomic_Store_64): Likewise.
* libgnat/s-atopri__32.ads (Atomic_Store): New generic procedure.
(Atomic_Store_8): New instantiated procedure.
(Atomic_Store_16): Likewise.
(Atomic_Store_32): Likewise.
* gcc-interface/decl.cc (gnat_to_gnu_subprog_type): Implement the
support for __atomic_store_n and __sync_bool_compare_and_swap_n.
* gcc-interface/gigi.h (list_second): New inline function.