lib.systems: Simplify ABI on POWER for rust.rustcTarget

Rust does not know how to parse "gnuabielfv{1,2}", so simplify those down to just "gnu".
This obsoletes the manual rustcTarget fix in the ppc64-elfv1 example.

lib/systems/default.nix

@@ -491,6 +491,13 @@ let
                 }
                 .${cpu.name} or cpu.name;
               vendor_ = final.rust.platform.vendor;
+              abi_ =
+                # We're very explicit about the POWER ELF ABI w/ glibc in our parsing, while Rust is not.
+                # TODO: Somehow ensure that Rust actually *uses* the correct ABI, and not just a libc-based default.
+                if (lib.strings.hasPrefix "powerpc" cpu.name) && (lib.strings.hasPrefix "gnuabielfv" abi.name) then
+                  "gnu"
+                else
+                  abi.name;
             in
             # TODO: deprecate args.rustc in favour of args.rust after 23.05 is EOL.
             args.rust.rustcTarget or args.rustc.config or (
@@ -501,7 +508,7 @@ let
               if final.isWasi then
                 "${cpu_}-wasip1"
               else
-                "${cpu_}-${vendor_}-${kernel.name}${optionalString (abi.name != "unknown") "-${abi.name}"}"
+                "${cpu_}-${vendor_}-${kernel.name}${optionalString (abi.name != "unknown") "-${abi_}"}"
             );
 
           # The name of the rust target if it is standard, or the json file