Truncate long TUI window titles

Truncate long TUI window titles

If a TUI window has a long title, it can overflow the title line.
This changes the TUI to use just the tail part of the title in this
case.

gdb/ChangeLog
2019-09-08  Tom Tromey  <tom@tromey.com>

	* tui/tui-wingeneral.c (box_win): Truncate long window titles.

gdb/testsuite/ChangeLog
2019-09-08  Tom Tromey  <tom@tromey.com>

	* gdb.tui/resize.exp: Remove setup_xfail.
	* gdb.tui/regs.exp: Remove setup_xfail.
	* gdb.tui/basic.exp: Remove setup_xfail.