Use scm_with_guile' in test-pthread-create'.

* test-suite/standalone/test-pthread-create.c (inner_main): New
  function.
  (main): Call it within `scm_with_guile', instead of using
  `scm_init_guile'.  This improves portability--e.g.,
  `GC_get_stack_base', used by `scm_init_guile', failed on Darwin
  up to BDW-GC 7.1alpha4 included (thanks, Mark, for the hint.)

test-suite/standalone/test-pthread-create.c

@@ -42,15 +42,12 @@ thread (void *arg)
   return NULL;
 }
 
-
-int
-main (int argc, char *argv[])
+static void *
+inner_main (void *data)
 {
   int i;
   pthread_t thr;
 
-  scm_init_guile ();
-
   do_something (NULL);
 
   for (i = 0; i < 77; i++)
@@ -59,5 +56,14 @@ main (int argc, char *argv[])
       pthread_join (thr, NULL);
     }
 
+  return NULL;
+}
+
+
+int
+main (int argc, char *argv[])
+{
+  scm_with_guile (inner_main, NULL);
+
   return EXIT_SUCCESS;
 }