Include what you use.

Don't rely on transitive includes. (Even though that works fine in AOSP.)

Change-Id: Ifc06575e4aea383cfff24d6c5c14fc0a7aabdf2b
diff --git a/tests/stdlib_test.cpp b/tests/stdlib_test.cpp
index 0bfb0c3..083e86a 100644
--- a/tests/stdlib_test.cpp
+++ b/tests/stdlib_test.cpp
@@ -24,6 +24,8 @@
 #include <stdint.h>
 #include <stdlib.h>
 #include <fcntl.h>
+#include <sys/types.h>
+#include <sys/wait.h>
 
 TEST(stdlib, drand48) {
   srand48(0x01020304);