WIFSIGNALED means process has exited too (with a bang!) (#5678)

tests/osproc/texitsignal.nim

@@ -0,0 +1,36 @@
+discard """
+  output: '''true
+true'''
+  targets: "c"
+"""
+
+import os, osproc
+when not defined(windows):
+  import posix
+
+# Checks that the environment is passed correctly in startProcess
+# To do that launches a copy of itself with a new environment.
+
+if paramCount() == 0:
+  # Parent process
+
+  let p = startProcess(
+    getAppFilename(),
+    args = @["child"],
+    options = {poStdErrToStdOut, poUsePath, poParentStreams}
+  )
+
+  echo p.running()
+
+  p.kill()
+
+  when defined(windows):
+    # windows kill happens using TerminateProcess(h, 0), so we should get a
+    # 0 here
+    echo p.waitForExit() == 0
+  else:
+    # on posix (non-windows), kill sends SIGKILL
+    echo p.waitForExit() == 128 + SIGKILL
+
+else:
+  sleep(5000)  # should get killed before this