Skip tests that require SIGPIPE when not supported

On MINGW, and probably native Windows, closing a pipe does not
send SIGPIPE to a child process, so tests that need SIGPIPE to
close the child process are skipped.

* test-suite/tests/popen.test
  ("no duplicate", "open-process"): skip if SIGPIPE unsupported
* test-suite/tests/ports.test ("pipe: write"): modify to use and
   awk script that terminates without SIGPIPE
* test-suite/tests/posix.test
  ("wc with stdin and stdout redirects"): skip if SIGPIPE unsupported
  ("awk with stdin and stdout redirects"): new test that doesn't require SIGPIPE

test-suite/tests/popen.test

@@ -200,6 +200,10 @@ exec 2>~a; read REPLY"
    ;; the child process; we rely on the child getting SIGPIPE, to
    ;; terminate it (and avoid leaving a zombie).
    (pass-if "no duplicate"
+     (unless (defined? 'SIGPIPE)
+       ;; MinGW has no SIGPIPE, so closing the pipe doesn't
+       ;; terminate the process.
+       (throw 'unsupported))
      (let* ((c2p (pipe))
             (port (with-error-to-port (cdr c2p)
                     (lambda ()
@@ -273,6 +277,10 @@ exec 2>~a; read REPLY"
 
 (pass-if-equal "open-process"
     '("HELLO WORLD" 0)
+  (unless (defined? 'SIGPIPE)
+    ;; MinGW has no SIGPIPE, so 'tr' doesn't exit when input is
+    ;; exhausted.
+    (throw 'unsupported))
   (receive (from to pid)
       ((@@ (ice-9 popen) open-process) OPEN_BOTH
        "tr" "[:lower:]" "[:upper:]")

test-suite/tests/ports.test

@@ -752,9 +752,14 @@
 
 
 ;;; Run a command, send some output to it, and see if it worked.
+
+;; We could have used grep for this test, but on systems without
+;; SIGPIPE, grep never exits.
 (pass-if "pipe: write"
   (let* ((filename (test-file))
-         (pipe (open-pipe (string-append "grep Mommy > " filename) "w")))
+         (awkscript
+          "awk 'BEGIN{i=1} {if (match($0,\"Mommy\")) print $0; if (i==2) exit; i++;}'")
+         (pipe (open-pipe (string-append awkscript " > " filename) "w")))
     (display "Now Jimmy lives on a mushroom cloud\n" pipe)
     (display "Mommy, why does everybody have a bomb?\n" pipe)
     (close-pipe pipe)

test-suite/tests/posix.test

@@ -422,8 +422,29 @@
         (close-port (car input+output))
         (list (cdr (waitpid pid)) str))))
 
+  (pass-if-equal "awk with stdin and stdout redirects"
+      "world.\n"
+    (let* ((a+b (pipe))
+           (c+d (pipe))
+           (pid (spawn "awk" '("awk" "{print $2; exit 0;}")
+                       #:input (car a+b)
+                       #:output (cdr c+d))))
+      (close-port (car a+b))
+      (close-port (cdr c+d))
+
+      (display "Hello world.\n" (cdr a+b))
+      (close-port (cdr a+b))
+
+      (let ((str (get-string-all (car c+d))))
+        (close-port (car c+d))
+        (waitpid pid)
+        str)))
+
   (pass-if-equal "wc with stdin and stdout redirects"
       "2\n"
+    (unless (defined? 'SIGPIPE)
+      ;; This test expects a closing pipe to kill the spawned process.
+      (throw 'unsupported))
     (let* ((a+b (pipe))
            (c+d (pipe))
            (pid (spawn "wc" '("wc" "-w")