Fix TUI test suite regexps

Fix TUI test suite regexps

Testing on another TUI series showed that some of the regexps in the
TUI test suite have been incorrect for a while.  In particular, "|"
was meant literally in these tests, but was interpreted as pattern
alternation due to lack of quoting.

This patch fixes the bad tests.  I am checking this in.

gdb/testsuite/ChangeLog
2019-12-11  Tom Tromey  <tom@tromey.com>

	* gdb.tui/resize.exp: Fix regexp.
	* gdb.tui/regs.exp: Fix regexps.
	* gdb.tui/main.exp: Fix regexp.

Change-Id: Ib6661361171ac120bb92f4a8aec7efa4bcaa36b9