Optimize scripts/merge-test-results.sh

The inner loop is called thousands of times per "make check" even
if there's otherwise nothing to do.  Avoid calling /bin/head all
those times when a builtin will do.

Reviewed-by: Carlos O'Donell <carlos@redhat.com>

scripts/merge-test-results.sh

@@ -35,7 +35,12 @@ case $type in
     subdir=${subdir:+$subdir/}
     for t in "$@"; do
       if [ -s "$objpfx$t.test-result" ]; then
-	head -n1 "$objpfx$t.test-result"
+	# This loop is called thousands of times even when there's
+	# nothing to do.  Avoid using non-built-in commands (like
+	# /bin/head) where possible.  We assume "echo" is typically a
+	# built-in.
+	IFS= read -r line < "$objpfx$t.test-result"
+	echo "$line"
       else
 	echo "UNRESOLVED: $subdir$t"
       fi