kexectools: Only build on kexecable architectures.

lib/systems/inspect.nix

@@ -35,6 +35,9 @@ rec {
     MinGW        = { kernel = kernels.windows; abi = abis.gnu; };
 
     Musl         = with abis; map (a: { abi = a; }) [ musl musleabi musleabihf ];
+
+    Kexecable    = map (family: { kernel = kernels.linux; cpu.family = family; })
+                     [ "x86" "arm" "aarch64" "mips" ];
   };
 
   matchAnyAttrs = patterns:

pkgs/top-level/all-packages.nix

@@ -3063,7 +3063,9 @@ with pkgs;
 
   keepalived = callPackage ../tools/networking/keepalived { };
 
-  kexectools = callPackage ../os-specific/linux/kexectools { };
+  kexectools = if hostPlatform.isKexecable
+                 then callPackage ../os-specific/linux/kexectools { }
+               else null;
 
   keybase = callPackage ../tools/security/keybase { };