gdb-testsuite-fix-race-in-gdb.threads-detach-step-over.exp

[gdb/testsuite] Fix race in gdb.threads/detach-step-over.exp

On OBS with openSUSE Leap 15.2 and target board unix/m32, I run into:
...
FAIL: gdb.threads/detach-step-over.exp: \
  breakpoint-condition-evaluation=host: target-non-stop=off: non-stop=off: \
  displaced=off: iter 1: all threads running
...

I can easily reproduce this by doing:
...

            # Wait a bit, to give time for the threads to hit the
            # breakpoint.
-           sleep 1

            set running_count 0
            set interrupted 0
...

Fix this by counting the running threads in a loop.

Tested on x86_64-linux.

---
 gdb/testsuite/gdb.threads/detach-step-over.exp | 26 +++++++++++++++++++++++---
 1 file changed, 23 insertions(+), 3 deletions(-)

diff --git a/gdb/testsuite/gdb.threads/detach-step-over.exp b/gdb/testsuite/gdb.threads/detach-step-over.exp
index 27718551188..d6fba07b486 100644
--- a/gdb/testsuite/gdb.threads/detach-step-over.exp
+++ b/gdb/testsuite/gdb.threads/detach-step-over.exp
@@ -203,7 +203,8 @@ proc test {condition_eval target_non_stop non_stop displaced} {
 
 	    set running_count 0
 	    set interrupted 0
-	    gdb_test_multiple "info threads" "all threads running" {
+	    set running_expected [expr ($n_threads + 1) * 2]
+	    gdb_test_multiple "info threads" "threads running" {
 		-re "\\(running\\)" {
 		    incr running_count
 		    exp_continue
@@ -224,10 +225,29 @@ proc test {condition_eval target_non_stop non_stop displaced} {
 			}
 		    }
 		}
-		-re "$gdb_prompt $" {
-		    gdb_assert {$running_count == ($n_threads + 1) * 2} $gdb_test_name
+		-re "$gdb_prompt " {
 		}
 	    }
+	    if { $interrupted == 0 } {
+		while { $running_count < $running_expected } {
+		    sleep 10
+		    set prev_running_count $running_count
+		    set running_count 0
+		    gdb_test_multiple "info threads" "threads running" {
+			-re "\\(running\\)" {
+			    incr running_count
+			    exp_continue
+			}
+			-re "$gdb_prompt $" {
+			}
+		    }
+		    if { $running_count == $prev_running_count } {
+			break
+		    }
+		}
+		gdb_assert {$running_count == $running_expected} \
+		    "all threads running"
+	    }
 
 	    gdb_test "detach" "Detaching from.*"