lib/systems: add SH4 (SuperH) cross-compilation target

Add sh4 CPU type (32-bit, little-endian, family "sh"), isSh4 predicate,
"sh4-linux" system double, cross-compilation example (sh4-unknown-linux-gnu),
linuxArch mapping to "sh", and test entry.

lib/systems/default.nix

@@ -300,6 +300,8 @@ let
             "powerpc"
           else if final.isRiscV then
             "riscv"
+          else if final.isSh4 then
+            "sh"
           else if final.isS390 then
             "s390"
           else if final.isLoongArch64 then

lib/systems/doubles.nix

@@ -40,6 +40,7 @@ let
     "i686-linux"
     "loongarch64-linux"
     "m68k-linux"
+    "sh4-linux"
     "microblaze-linux"
     "microblazeel-linux"
     "mips-linux"
@@ -145,6 +146,7 @@ in
   or1k = filterDoubles predicates.isOr1k;
   m68k = filterDoubles predicates.isM68k;
   arc = filterDoubles predicates.isArc;
+  sh4 = filterDoubles predicates.isSh4;
   s390 = filterDoubles predicates.isS390;
   s390x = filterDoubles predicates.isS390x;
   loongarch64 = filterDoubles predicates.isLoongArch64;

lib/systems/examples.nix

@@ -243,6 +243,10 @@ rec {
     config = "arc-unknown-linux-gnu";
   };
 
+  sh4 = {
+    config = "sh4-unknown-linux-gnu";
+  };
+
   s390 = {
     config = "s390-unknown-linux-gnu";
   };

lib/systems/inspect.nix

@@ -234,6 +234,11 @@ rec {
         family = "arc";
       };
     };
+    isSh4 = {
+      cpu = {
+        family = "sh";
+      };
+    };
     isS390 = {
       cpu = {
         family = "s390";

lib/systems/parse.nix

@@ -284,6 +284,12 @@ rec {
         family = "m68k";
       };
 
+      sh4 = {
+        bits = 32;
+        significantByte = littleEndian;
+        family = "sh";
+      };
+
       powerpc = {
         bits = 32;
         significantByte = bigEndian;

lib/tests/systems.nix

@@ -171,6 +171,7 @@ lib.runTests (
       "i686-linux"
       "loongarch64-linux"
       "m68k-linux"
+      "sh4-linux"
       "microblaze-linux"
       "microblazeel-linux"
       "mips-linux"