CI: Test & fix Linux ZFS built-in build

ZFS can be built directly into the Linux kernel.  Add a test build
of this to the CI to verify it works.  The test build is only enabled
on Fedora runners (since they run the newest kernels) and is done in
parallel with ZTS.  The test build is done on vm2, since it typically
finishes ~15min before vm1 and thus has time to spare.

In addition:

- Update 'copy-builtin' to check that $1 is a directory
- Fix some VERIFYs that were causing the built-in build to fail

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Tony Hutter <hutter2@llnl.gov>
Closes #18234

.github/workflows/scripts/qemu-8-summary.sh

@@ -33,7 +33,7 @@ EOF
 
 function showfile_tail() {
   echo "##[group]$2 (final lines)"
-  tail -n 40 $1
+  tail -n 80 $1
   echo "##[endgroup]"
 }
 
@@ -66,6 +66,18 @@ for ((i=1; i<=VMs; i++)); do
     test -s "$file" && showfile_tail "$file" "$vm: Lustre build"
   fi
 
+  if [ -f vm$i/builtin-exitcode.txt ] ; then
+    rv=$(< vm$i/builtin-exitcode.txt)
+    if [ $rv = 0 ]; then
+      vm="vm$i"
+    else
+      vm="vm$i"
+      touch /tmp/have_failed_tests
+    fi
+    file="vm$i/builtin.txt"
+    test -s "$file" && showfile_tail "$file" "$vm: Linux built-in build"
+  fi
+
   rv=$(cat vm$i/tests-exitcode.txt)
 
   if [ $rv = 0 ]; then