[gdb/testsuite] Fix gdb.tui/completion.exp for local-remote-host-notty

When running test-case gdb.tui/completion.exp with host board
local-remote-host-notty and target board native-gdbserver, I get:
...
FAIL: gdb.tui/completion.exp: completion of layout names: \
  tab completion (timeout)
...

The test-case contains a few tests that do tab completion, which requires
readline, which is unavailable with host board local-remote-host-notty.

Fix this by adding the missing check for readline_is_used.

Tested on x86_64-linux.

1 files changed, 8 insertions, 5 deletions

diff --git a/gdb/testsuite/gdb.tui/completion.exp b/gdb/testsuite/gdb.tui/completion.exp
index 0a959b4..85abd4a 100644
--- a/gdb/testsuite/gdb.tui/completion.exp
+++ b/gdb/testsuite/gdb.tui/completion.exp
@@ -48,12 +48,15 @@ proc test_tab_completion {input_line expected_re} {
     }
 }
 
-with_test_prefix "completion of layout names" {
-    test_tab_completion "layout" "asm *next *prev *regs *split *src *"
-}
+if { [readline_is_used] } {
+    with_test_prefix "completion of layout names" {
+	test_tab_completion "layout" "asm *next *prev *regs *split *src *"
+    }
 
-with_test_prefix "completion of focus command" {
-    test_tab_completion "focus" "cmd *next *prev *src *"
+
+    with_test_prefix "completion of focus command" {
+	test_tab_completion "focus" "cmd *next *prev *src *"
+    }
 }
 
 # Now run some completion tests when TUI mode is enabled.