Add the Missing Header

`stderror` is used in this file and it is defined in `string.h/cstring`, so
the header file needs to be directly included.

Test: build
Bug: 285204695
Change-Id: Idf34126626ad0e9bb397df3d5da50439bf18381d
diff --git a/libutils/Errors.cpp b/libutils/Errors.cpp
index 74f3bef..dfb4d9b 100644
--- a/libutils/Errors.cpp
+++ b/libutils/Errors.cpp
@@ -15,6 +15,8 @@
  */
 #include <utils/Errors.h>
 
+#include <string.h>
+
 namespace android {
 
 std::string statusToString(status_t s) {