[gdb/testsuite] Add gdb.base/color-prompt.exp

After updating the documentation in commit cf03713dd1c ("[gdb/cli] Document
\001 and \002 usage for set prompt"), I started to wonder if I could reproduce
the CLI issue described in PR cli/28887 using the TUI.

That turned out not to be the case, but I noticed handling of the markers in
tui_puts and tui_puts_internal, and no test-case exercising this, so I
decided to add this.

After doing so in gdb.tui/color-prompt.exp, I realized I could use the same
code to test the CLI case.

Add test-case gdb.base/color-prompt.exp that shares code with
gdb.tui/color-prompt.exp in gdb.tui/color-prompt.exp.tcl.

For the CLI case, I was hoping to reproduce the behaviour described in the PR,
but it didn't trigger.

FTR, I manually reproduced the behaviour and used script to record it.  I
observed the following sequence after the C-a:
- ^M (CR)             : go to start of line
- ^[[K (EL)           : erase line
- ^M (CR)             : go to start of line
- ^[[31m(gdb) ^[[0m   : output prompt
- some long command   : output text
- ^M (CR)             : go to start of line
- ^[[C, 15 times (CUF): cursor forward 15 times
giving me:
...
(gdb) some long command
               ^
...

Perhaps we'll trigger this on some other os, or once we start using a
different TERM value.

Tested on x86_64-linux.

1 files changed, 29 insertions, 0 deletions

diff --git a/gdb/testsuite/gdb.base/color-prompt.exp b/gdb/testsuite/gdb.base/color-prompt.exp
new file mode 100644
index 0000000..c037185
--- /dev/null
+++ b/gdb/testsuite/gdb.base/color-prompt.exp
@@ -0,0 +1,29 @@
+# Copyright 2025 Free Software Foundation, Inc.
+
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+# Check using a prompt with color in CLI.
+
+# Using tuiterm requires setting TERM on host.
+require {!is_remote host}
+
+# We use a tuiterm, which allows us to determine cursor position.
+tuiterm_env
+Term::clean_restart 8 80
+
+# We start with an empty screen, to generate a visible prompt.
+Term::gen_prompt
+
+set tui 0
+source $srcdir/$subdir/../gdb.tui/color-prompt.exp.tcl