[gdb/testsuite] Fix gdb.tui/long-prompt.exp with read1

When running test-case gdb.tui/long-prompt.exp with check-read1, we get:
...
(gdb) FAIL: gdb.tui/long-prompt.exp: prompt size == width + 1: \
  end of screen: at last line
...

The problem is in these commands:
...
    Term::command "echo \\n"
    Term::command "echo \\n"
    Term::command "echo \\n"
    Term::command "echo \\n"
...

The last one makes the terminal scroll, and the scrolling makes the expected
output match on a different line.

Fix this by replacing the sequence with a single command:
...
    Term::command "echo \\n\\n\\n\\n\\n\\n"
...
which avoids scrolling.

Tested on x86_64-linux.

1 files changed, 1 insertions, 4 deletions

diff --git a/gdb/testsuite/gdb.tui/long-prompt.exp b/gdb/testsuite/gdb.tui/long-prompt.exp
index e7249bb..e4e8b75 100644
--- a/gdb/testsuite/gdb.tui/long-prompt.exp
+++ b/gdb/testsuite/gdb.tui/long-prompt.exp
@@ -57,10 +57,7 @@ with_test_prefix "prompt size == width + 1: end of screen" {
     }
 
     # Put prompt at last line.
-    Term::command "echo \\n"
-    Term::command "echo \\n"
-    Term::command "echo \\n"
-    Term::command "echo \\n"
+    Term::command "echo \\n\\n\\n\\n\\n\\n"
     gdb_assert { $Term::_cur_row == 23 } "at last line"
 
     set prompt "123456789A123456789B123456789C123456789D>"