make-iso9660-image: produce stable GPT disk GUID

By generating a version-5 GUID based on $out (which contains
the derivation hash) and preventing isohybrid from overwriting
the GPT table (which already is populated correctly by xorriso).

Tested by:
* booting from USB disk on a UEFI system
* booting from USB disk on a non-UEFI system
* booting from CD on a UEFI system
* booting from CD on a non-UEFI system
* booting from CD on an OSX system

Also tested that "nix-build ./nixos/release-combined.nix -A
nixos.iso_minimal.x86_64-linux -I nixpkgs=~/nixpkgs-r13y --check"
now succeeds.

Fixes #74047

nixos/lib/make-iso9660-image.sh

@@ -99,7 +99,12 @@ done
 
 mkdir -p $out/iso
 
+# daed2280-b91e-42c0-aed6-82c825ca41f3 is an arbitrary namespace, to prevent
+# independent applications from generating the same UUID for the same value.
+# (the chance of that being problematic seem pretty slim here, but that's how
+# version-5 UUID's work)
 xorriso="xorriso
+ -boot_image any gpt_disk_guid=$(uuid -v 5 daed2280-b91e-42c0-aed6-82c825ca41f3 $out | tr -d -)
  -as mkisofs
  -iso-level 3
  -volid ${volumeID}
@@ -118,15 +123,6 @@ xorriso="xorriso
 
 $xorriso -output $out/iso/$isoName
 
-if test -n "$usbBootable"; then
-    echo "Making image hybrid..."
-    if test -n "$efiBootable"; then
-        isohybrid --uefi $out/iso/$isoName
-    else
-        isohybrid $out/iso/$isoName
-    fi
-fi
-
 if test -n "$compressImage"; then
     echo "Compressing image..."
     zstd -T$NIX_BUILD_CORES --rm $out/iso/$isoName