Skip ports tests that require popen if popen not available

* test-suite/tests/ports.test (define-module): don't use (ice-9 popen)
  (if-supported): new syntax
  (pipe:write, pipe:write): disable if no popen provided
  (line-counter): disable if no popen provided

test-suite/tests/ports.test

@@ -21,7 +21,6 @@
 (define-module (test-suite test-ports)
   #:use-module (test-suite lib)
   #:use-module (test-suite guile-test)
-  #:use-module (ice-9 popen)
   #:use-module (ice-9 rdelim)
   #:use-module (ice-9 threads)
   #:use-module (rnrs bytevectors)
@@ -618,6 +617,13 @@
 
 ;;;; Pipe (popen) ports.
 
+(define-syntax-rule (if-supported body ...)
+  (when (provided? 'popen)
+        (begin body ...)))
+
+(if-supported
+ (use-modules (ice-9 popen))
+
 ;;; Run a command, and read its output.
  (let* ((pipe (open-pipe "echo 'Howdy there, partner!'" "r"))
         (in-string (read-all pipe)))
@@ -634,7 +640,7 @@
    (let ((in-string (read-file filename)))
      (pass-if "pipe: write"
        (equal? in-string "Mommy, why does everybody have a bomb?\n")))
-  (delete-file filename))
+   (delete-file filename)))
 
 (pass-if-equal "pipe, fdopen, and line buffering"
     "foo\nbar\n"
@@ -1020,6 +1026,7 @@
 
 ;;;; Generic operations across all port types.
 
+(if-supported
  (let ((port-loop-temp (test-file)))
 
    ;; Return a list of input ports that all return the same text.
@@ -1093,7 +1100,7 @@
                      "  --- Thomas Jefferson\n"
                      "no newline here")
       "He who receives an idea from me, receives instruction"
-     15)))
+      15))))
 
 ;; Test port-line and port-column for output ports