Fix @multitable handling in texi2pod.pl

While trying out Dennis's Armv8.6-A patch, I noticed that texi2pod.pl
didn't handle the new @multitable correctly.  There were two problems:

(1) @multitables nested in other @tables inherited the @item type from
    the enclosing @table.  Since the new @multitable is in a @table @samp,
    we applied @samp markup to the @multitable @items.  This in turn
    meant that it captured the @tab separator in the @item markup.

    Fixed by pushing an empty item code onto the stack.

(2) We didn't handle @headitem.  Fixed by enclosing it in italics,
    like we do for section headings.  This causes it to be underlined
    in the man output.

2019-12-07  Richard Sandiford  <richard.sandiford@arm.com>

contrib/
	* texi2pod.pl: Handle @headitems in @multitables, printing them
	in italics.  Push an empty item code onto the stack.

From-SVN: r279074

contrib/ChangeLog

+2019-12-07  Richard Sandiford  <richard.sandiford@arm.com>
+
+	* texi2pod.pl: Handle @headitems in @multitables, printing them
+	in italics.  Push an empty item code onto the stack.
+
 2019-11-13  Janne Blomqvist  <jb@gcc.gnu.org>
 
 	* download_prerequisites: Use http instead of ftp for downloading.

contrib/texi2pod.pl

@@ -164,6 +164,7 @@ while(<$inf>) {
 	    $ic = pop @icstack;
 	} elsif ($ended eq "multitable") {
 	    $_ = "\n=back\n";
+	    $ic = pop @icstack;
 	} else {
 	    die "unknown command \@end $ended at line $.\n";
 	}
@@ -288,7 +289,9 @@ while(<$inf>) {
 
     /^\@multitable\s.*/ and do {
 	push @endwstack, $endw;
+	push @icstack, $ic;
 	$endw = "multitable";
+	$ic = "";
 	$_ = "\n=over 4\n";
     };
 
@@ -312,11 +315,13 @@ while(<$inf>) {
 	$_ = "";	# need a paragraph break
     };
 
-    /^\@item\s+(.*\S)\s*$/ and $endw eq "multitable" and do {
+    /^\@(headitem|item)\s+(.*\S)\s*$/ and $endw eq "multitable" and do {
 	@columns = ();
-	for $column (split (/\s*\@tab\s*/, $1)) {
+	$item = $1;
+	for $column (split (/\s*\@tab\s*/, $2)) {
 	    # @strong{...} is used a @headitem work-alike
 	    $column =~ s/^\@strong\{(.*)\}$/$1/;
+	    $column = "I<$column>" if $item eq "headitem";
 	    push @columns, $column;
 	}
 	$_ = "\n=item ".join (" : ", @columns)."\n";