Factor out the waiting for children in bionic tests.

Change-Id: I4a1e51b6920b33dc892d447f5bd6d10f1cb2704a
diff --git a/tests/stdlib_test.cpp b/tests/stdlib_test.cpp
index 050f5a7..6ae6cda 100644
--- a/tests/stdlib_test.cpp
+++ b/tests/stdlib_test.cpp
@@ -15,8 +15,10 @@
  */
 
 #include <gtest/gtest.h>
+
 #include "BionicDeathTest.h"
 #include "TemporaryFile.h"
+#include "utils.h"
 
 #include <errno.h>
 #include <libgen.h>
@@ -323,10 +325,7 @@
     quick_exit(99);
   }
 
-  int status;
-  ASSERT_EQ(pid, waitpid(pid, &status, 0));
-  ASSERT_TRUE(WIFEXITED(status));
-  ASSERT_EQ(99, WEXITSTATUS(status));
+  AssertChildExited(pid, 99);
 }
 
 static int quick_exit_status = 0;
@@ -355,24 +354,18 @@
     quick_exit(99);
   }
 
-  int status;
-  ASSERT_EQ(pid, waitpid(pid, &status, 0));
-  ASSERT_TRUE(WIFEXITED(status));
-  ASSERT_EQ(99, WEXITSTATUS(status));
+  AssertChildExited(pid, 99);
 }
 
 TEST(unistd, _Exit) {
-  int pid = fork();
+  pid_t pid = fork();
   ASSERT_NE(-1, pid) << strerror(errno);
 
   if (pid == 0) {
     _Exit(99);
   }
 
-  int status;
-  ASSERT_EQ(pid, waitpid(pid, &status, 0));
-  ASSERT_TRUE(WIFEXITED(status));
-  ASSERT_EQ(99, WEXITSTATUS(status));
+  AssertChildExited(pid, 99);
 }
 
 TEST(stdlib, pty_smoke) {