Move waitpid(2) includes to art::Exec implementation

(cherry picked from commit 446a13ff04dae7ef9c90584e7cf8e834ee841681)

Change-Id: Id5fe3dd8e6c4cef953c39b00f2a53b23da5a6247
diff --git a/runtime/class_linker.cc b/runtime/class_linker.cc
index 1c721c9..69d957f 100644
--- a/runtime/class_linker.cc
+++ b/runtime/class_linker.cc
@@ -19,8 +19,6 @@
 #include <fcntl.h>
 #include <sys/file.h>
 #include <sys/stat.h>
-#include <sys/types.h>
-#include <sys/wait.h>
 
 #include <deque>
 #include <string>
diff --git a/runtime/gc/space/image_space.cc b/runtime/gc/space/image_space.cc
index 86dee1d..12c5451 100644
--- a/runtime/gc/space/image_space.cc
+++ b/runtime/gc/space/image_space.cc
@@ -16,9 +16,6 @@
 
 #include "image_space.h"
 
-#include <sys/types.h>
-#include <sys/wait.h>
-
 #include "base/stl_util.h"
 #include "base/unix_file/fd_file.h"
 #include "gc/accounting/space_bitmap-inl.h"
diff --git a/runtime/utils.cc b/runtime/utils.cc
index 39a051c..68d8417 100644
--- a/runtime/utils.cc
+++ b/runtime/utils.cc
@@ -21,6 +21,8 @@
 #include <sys/stat.h>
 #include <sys/syscall.h>
 #include <sys/types.h>
+#include <sys/wait.h>
+
 #include <unistd.h>
 
 #include "UniquePtr.h"