Two fixes for test suite's terminal

Exactly which escape sequences are emitted by gdb in TUI mode are
determined largely by the curses implementation.  Testing my latest
(as yet unsubmitted) series to refactor the TUI showed a couple of
failures that I tracked to the test suite's terminal implementation.

In particular, the CSI "@" sequence was not implemented; and the CSI
"X" sequence was implemented incorrectly.

This patch fixes both of these problems.  Tested on x86-64 Fedora 28.

gdb/testsuite/ChangeLog
2019-07-29  Tom Tromey  <tom@tromey.com>

	* lib/tuiterm.exp (Term::_csi_@): New proc.
	(Term::_csi_X): Don't move cursor.

gdb/testsuite/ChangeLog

@@ -1,3 +1,8 @@
+2019-07-29  Tom Tromey  <tom@tromey.com>
+
+	* lib/tuiterm.exp (Term::_csi_@): New proc.
+	(Term::_csi_X): Don't move cursor.
+
 2019-07-29  Philippe Waroquiers  <philippe.waroquiers@skynet.be>
 
 	* gdb.base/options.exp: Update backtrace - completion to

gdb/testsuite/lib/tuiterm.exp

@@ -104,6 +104,21 @@ namespace eval Term {
 	set _cur_x 0
     }
 
+    # Make room for characters.
+    proc _csi_@ {args} {
+	set n [_default [lindex $args 0] 1]
+	variable _cur_x
+	variable _cur_y
+	variable _chars
+	set in_x $_cur_x
+	set out_x [expr {$_cur_x + $n}]
+	for {set i 0} {$i < $n} {incr i} {
+	    set _chars($out_x,$_cur_y) $_chars($in_x,$_cur_y)
+	    incr in_x
+	    incr out_x
+	}
+    }
+
     # Cursor Up.
     proc _csi_A {args} {
 	variable _cur_y
@@ -238,7 +253,17 @@ namespace eval Term {
     # Erase chars.
     proc _csi_X {args} {
 	set n [_default [lindex $args 0] 1]
-	_insert [string repeat " " $n]
+	# Erase characters but don't move cursor.
+	variable _cur_x
+	variable _cur_y
+	variable _attrs
+	variable _chars
+	set lattr [array get _attrs]
+	set x $_cur_x
+	for {set i 0} {$i < $n} {incr i} {
+	    set _chars($x,$_cur_y) [list " " $lattr]
+	    incr x
+	}
     }
 
     # Repeat.