Fix 'typeset -p' output of compound array types (#453)

This bugfix was backported from ksh93v- 2012-10-04. The bug fixed
by this change is one that causes 'typeset -p' to omit the -C flag
when listing compound arrays belonging to a type:

   $ typeset -T Foo_t=(compound -a bar)
   $ Foo_t baz
   $ typeset -p baz.bar
   typeset -a baz.bar=''  # This should be 'typeset -C -a'

src/cmd/ksh93/sh/nvtype.c:
- Backport change from 93v- 2012-10-04 that sets the array nvalue to
  a pointer named Null (which is "") in nv_mktype(), then to Empty
  in fixnode().
- Change the Null name from the 93v- code to AltEmpty to avoid
  misleading code readers into thinking that it's a null pointer.

src/cmd/ksh93/tests/types.sh:
- Backport the relevant 93v- changes to the types regression tests.

Co-authored-by: Martijn Dekker <martijn@inlv.org>

src/cmd/ksh93/tests/types.sh

@@ -592,7 +592,7 @@ $SHELL << \EOF
 			 compound p=( hello=world )
 			 c.b.binsert p 1 $i
 		done
-		exp='typeset -C c=(board_t b=(typeset -a board_y=( [1]=(typeset -a board_x=( [0]=(field=(hello=world;))[1]=(field=(hello=world)));));))'
+		exp='typeset -C c=(board_t b=(typeset -C -a board_y=( [1]=(typeset -a board_x=( [0]=(field=(hello=world;))[1]=(field=(hello=world)));));))'
 		[[ $(typeset -p c) == "$exp" ]] || exit 1
 	}
 	main
@@ -634,6 +634,13 @@ Bar_t bar
 bar.foo+=(bam)
 [[ ${bar.foo[0]} == bam ]] || err_exit 'appending to empty array variable in type does not create element 0'
 
+# ======
+# Compound arrays listed with 'typeset -p' should have their -C attribute
+# preserved in the output.
+typeset -T Z_t=(compound -a x)
+Z_t z
+[[ $(typeset -p z.x) ==  *'-C -a'* ]] || err_exit 'typeset -p for compound array element does not display all attributes'
+
 # ======
 # Type names that have 'a' as the first letter should be functional
 "$SHELL" -c 'typeset -T al=(typeset bar); al foo=(bar=testset)' || err_exit "type names that start with 'a' don't work"