Fix C++23 build.

libc++ is stricter about transitive includes when you're building as
C++23.

Change-Id: Ib553d26cf7ce14bbc8624595904dc1bb64be56d6

icing/text_classifier/lib3/utils/base/statusor.h

diff --git a/icing/text_classifier/lib3/utils/base/statusor.h b/icing/text_classifier/lib3/utils/base/statusor.h
index aa1e598..4d9bb71 100644
--- a/icing/text_classifier/lib3/utils/base/statusor.h
+++ b/icing/text_classifier/lib3/utils/base/statusor.h
@@ -15,6 +15,7 @@
 #ifndef ICING_TEXT_CLASSIFIER_LIB3_UTILS_BASE_STATUSOR_H_
 #define ICING_TEXT_CLASSIFIER_LIB3_UTILS_BASE_STATUSOR_H_
 
+#include <cstdlib>
 #include <type_traits>
 #include <utility>