Fix build: include what you use.

Change-Id: I12b2d5e434ad3ed38d4451bd470673781e6ca8fe
diff --git a/tests/unistd_test.cpp b/tests/unistd_test.cpp
index da8fd4b..f56c5da 100644
--- a/tests/unistd_test.cpp
+++ b/tests/unistd_test.cpp
@@ -22,6 +22,8 @@
 #include <fcntl.h>
 #include <stdint.h>
 #include <unistd.h>
+#include <sys/types.h>
+#include <sys/wait.h>
 
 TEST(unistd, sysconf_SC_MONOTONIC_CLOCK) {
   ASSERT_GT(sysconf(_SC_MONOTONIC_CLOCK), 0);