Fix for gdb.tui/tui-layout-asm.exp

Fix for gdb.tui/tui-layout-asm.exp

The width of the window is too narrow to display the entire assembly line.
The width of the columns in the window changes as the test walks thru the
terminal window output.  The column change results in the first and second
reads of the same line to differ thus causing the test to fail.  Increasing
the width of the window keeps the column width consistent thru the test.

If the test fails, the added check prints an message to the log file if
the failure may be due to the window being too narrow.

gdb/testsuite/ChangeLog

	* gdb.tui/tui-layout-asm.exp: Replace window width of 80 with the
	tui_asm_window_width variable for the width. Add if
	count_whitespace check.
	(count_whitespace): New proc