[libc++][NFC] Add missing include to ext/__hash

Note that we use <stddef.h> instead of <cstddef> because we're
using size_t (not std::size_t) and we're outside of namespace std.

Differential Revision: https://reviews.llvm.org/D138716

diff --git a/libcxx/include/ext/__hash b/libcxx/include/ext/__hash
index 0e6c2cc..880d0ee 100644 (file)
--- a/libcxx/include/ext/__hash
+++ b/libcxx/include/ext/__hash
@@ -14,6 +14,7 @@
 
 #include <__config>
 #include <cstring>
+#include <stddef.h>
 #include <string>
 
 namespace __gnu_cxx {