[Ada] Expose and use type-generic GCC atomic builtins

[Pierre-Marie de Rodat via Gcc-patches]

This exposes the newly added support for type-generic GCC atomic builtins
to the user through the System.Atomic_Primitives package, where a generic
version of the existing routines is added.  This also uses this support
in the implementation of the System.Atomic_Operations packages.

Tested on x86_64-pc-linux-gnu, committed on trunk

gcc/ada/

        * sem_ch12.adb (Analyze_Subprogram_Instantiation): Also propagate an
        interface name on an intrinsic subprogram.  Remove obsolete comment.
        * libgnat/s-atopri.ads (Atomic_Load): New generic intrinsic function
        (Atomic_Load_8): Rewrite into instantiation.
        (Atomic_Load_16): Likewise.
        (Atomic_Load_32): Likewise.
        (Atomic_Load_64): Likewise.
        (Sync_Compare_And_Swap): New generic intrinsic function.
        (Sync_Compare_And_Swap_8): Rewrite into instantiation.
        (Sync_Compare_And_Swap_16): Likewise.
        (Sync_Compare_And_Swap_32): Likewise.
        (Sync_Compare_And_Swap_64): Likewise.
        (Lock_Free_Read): New generic inline function.
        (Lock_Free_Read_8): Rewrite into instantiation.
        (Lock_Free_Read_16): Likewise.
        (Lock_Free_Read_32): Likewise.
        (Lock_Free_Read_64): Likewise.
        (Lock_Free_Try_Write): New generic inline function.
        (Lock_Free_Try_Write_8): Rewrite into instantiation.
        (Lock_Free_Try_Write_16): Likewise.
        (Lock_Free_Try_Write_32): Likewise.
        (Lock_Free_Try_Write_64): Likewise.
        * libgnat/s-atopri.adb (Lock_Free_Read): New function body.
        (Lock_Free_Read_8): Delete.
        (Lock_Free_Read_16): Likewise.
        (Lock_Free_Read_32): Likewise.
        (Lock_Free_Read_64): Likewise.
        (Lock_Free_Try_Write): New function body.
        (Lock_Free_Try_Write_8): Delete.
        (Lock_Free_Try_Write_16): Likewise.
        (Lock_Free_Try_Write_32): Likewise.
        (Lock_Free_Try_Write_64): Likewise.
        * libgnat/s-aoinar.adb (Atomic_Fetch_And_Add): Use type-generic GCC
        atomic builtin and tidy up implementation.
        (Atomic_Fetch_And_Subtract): Likewise.
        * libgnat/s-aomoar.adb (Atomic_Fetch_And_Add): Likewise.
        (Atomic_Fetch_And_Subtract): Likewise.
        * libgnat/s-atopex.adb (Atomic_Exchange): Likewise.
        (Atomic_Compare_And_Exchange): Likewise.

patch.diff.gz
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