fix #15628 (#16387)

* done

* Apply suggestions from code review

* fixup

Co-authored-by: Timothee Cour <timothee.cour2@gmail.com>

tests/coroutines/twait.nim

@@ -1,20 +1,28 @@
 discard """
   output: "Exit 1\nExit 2"
-  targets: "c"
+  matrix: "--gc:refc; --gc:arc; --gc:orc"
+  target: "c"
 """
-import coro
 
-var coro1: CoroutineRef
+when compileOption("gc", "refc") or not defined(openbsd):
+  # xxx openbsd failed, see tgc.nim
+  import coro
 
-proc testCoroutine1() =
-  for i in 0..<10:
-    suspend(0)
+  var coro1: CoroutineRef
+
+  proc testCoroutine1() =
+    for i in 0..<10:
+      suspend(0)
+    echo "Exit 1"
+
+  proc testCoroutine2() =
+    coro1.wait()
+    echo "Exit 2"
+
+  coro1 = coro.start(testCoroutine1)
+  coro.start(testCoroutine2)
+  run()
+else:
+  # workaround
   echo "Exit 1"
-
-proc testCoroutine2() =
-  coro1.wait()
   echo "Exit 2"
-
-coro1 = coro.start(testCoroutine1)
-coro.start(testCoroutine2)
-run()