Install clang on 21.04 or later

Don't drop clang from 21.04 containers, that breaks existing scripts
that use the 21.04 container for clang builds.

Fixes: 7ddd70d ("Add Ubuntu 21.10 and use it in preference to 21.04")

Author: mpe

build/ubuntu/packages.sh

@@ -6,11 +6,9 @@ machine=$(uname -m)
 
 . /etc/os-release
 
-if [[ "$VERSION_ID" == "21.10" ]]; then
-    if [[ "$machine" != "x86_64" ]]; then
-        PACKAGES+=" crossbuild-essential-amd64"
-    fi
+major="${VERSION_ID%%.*}"
 
+if [[ "$major" -ge 21 ]]; then
     PACKAGES+=" clang llvm"
 fi
 
@@ -22,6 +20,11 @@ if [[ "$machine" == "ppc64le" ]]; then
     PACKAGES+=" libhugetlbfs-dev"
     PACKAGES+=" libmnl-dev"
     PACKAGES+=" libmount-dev"
+
+    # For the x86_64 container
+    if [[ "$VERSION_ID" == "21.10" ]]; then
+        PACKAGES+=" crossbuild-essential-amd64"
+    fi
 else
     PACKAGES+=" gcc-powerpc64le-linux-gnu g++-powerpc64le-linux-gnu"
 fi