lib/systems: add ARC (Synopsys DesignWare ARC) cross-compilation support

Add arc CPU type (32-bit, little-endian, family "arc"), isArc
predicate, arc-linux double, arc cross example with
arc-unknown-linux-gnu triple, and release-cross job.

ARC has glibc support and uses the "arc" Linux kernel arch, which
matches the CPU name so no explicit linuxArch mapping is needed.

lib/systems/doubles.nix

@@ -32,6 +32,7 @@ let
 
     # Linux
     "aarch64-linux"
+    "arc-linux"
     "armv5tel-linux"
     "armv6l-linux"
     "armv7a-linux"
@@ -143,6 +144,7 @@ in
   vc4 = filterDoubles predicates.isVc4;
   or1k = filterDoubles predicates.isOr1k;
   m68k = filterDoubles predicates.isM68k;
+  arc = filterDoubles predicates.isArc;
   s390 = filterDoubles predicates.isS390;
   s390x = filterDoubles predicates.isS390x;
   loongarch64 = filterDoubles predicates.isLoongArch64;

lib/systems/examples.nix

@@ -239,6 +239,10 @@ rec {
     config = "m68k-unknown-linux-gnu";
   };
 
+  arc = {
+    config = "arc-unknown-linux-gnu";
+  };
+
   s390 = {
     config = "s390-unknown-linux-gnu";
   };

lib/systems/inspect.nix

@@ -229,6 +229,11 @@ rec {
         family = "m68k";
       };
     };
+    isArc = {
+      cpu = {
+        family = "arc";
+      };
+    };
     isS390 = {
       cpu = {
         family = "s390";

lib/systems/parse.nix

@@ -382,6 +382,12 @@ rec {
         family = "or1k";
       };
 
+      arc = {
+        bits = 32;
+        significantByte = littleEndian;
+        family = "arc";
+      };
+
       loongarch64 = {
         bits = 64;
         significantByte = littleEndian;

lib/tests/systems.nix

@@ -163,6 +163,7 @@ lib.runTests (
     testillumos = mseteq illumos [ "x86_64-solaris" ];
     testlinux = mseteq linux [
       "aarch64-linux"
+      "arc-linux"
       "armv5tel-linux"
       "armv6l-linux"
       "armv7a-linux"

pkgs/top-level/release-cross.nix

@@ -250,6 +250,7 @@ in
   loongarch64-linux = mapTestOnCross systems.examples.loongarch64-linux linuxCommon;
 
   m68k = mapTestOnCross systems.examples.m68k linuxCommon;
+  arc = mapTestOnCross systems.examples.arc linuxCommon;
   s390x = mapTestOnCross systems.examples.s390x linuxCommon;
 
   # (Cross-compiled) Linux on x86