Replace GCC-only `std::_Identity` and `std::_Select1st` with own code

Put in `stllike` submodule since it's technically hoisted from _a_
STL implementation...!
`vespalib::Identity` can be replaced with `std::identity` once on
a C++20 compiler.

1 files changed, 2 insertions, 1 deletions

diff --git a/vespalib/src/tests/stllike/hashtable_test.cpp b/vespalib/src/tests/stllike/hashtable_test.cpp
index 4948faf450f..877a5dddcb5 100644
--- a/vespalib/src/tests/stllike/hashtable_test.cpp
+++ b/vespalib/src/tests/stllike/hashtable_test.cpp
@@ -3,6 +3,7 @@
 
 #include <vespa/vespalib/stllike/hashtable.hpp>
 #include <vespa/vespalib/stllike/hash_fun.h>
+#include <vespa/vespalib/stllike/identity.h>
 #include <vespa/vespalib/testkit/testapp.h>
 #include <memory>
 #include <vector>
@@ -63,7 +64,7 @@ TEST("require that hashtable can store pairs of <key, unique_ptr to value>") {
 }
 
 template<typename K> using set_hashtable =
-    hashtable<K, K, vespalib::hash<K>, std::equal_to<K>, std::_Identity<K>>;
+    hashtable<K, K, vespalib::hash<K>, std::equal_to<K>, Identity>;
 
 TEST("require that hashtable<int> can be copied") {
     set_hashtable<int> table(100);