Revert "[Minor] C++20 is here"

This change is not so useful to break compatibility with Clang 7. Maybe later...

This reverts commit 48ce799a7a.

src/client/rspamc.cxx

@@ -427,6 +427,12 @@ static const auto sort_map = frozen::make_unordered_map<frozen::string, sort_lam
 		}},
 });
 
+/* TODO: remove once migrate to C++20 standard */
+static constexpr auto
+sv_ends_with(std::string_view inp, std::string_view suffix) -> bool {
+	return inp.size() >= suffix.size() && inp.compare(inp.size() - suffix.size(), std::string_view::npos, suffix) == 0;
+}
+
 template<typename T>
 auto sort_ucl_container_with_default(T &cont, const char *default_sort,
 									 typename std::enable_if<std::is_same_v<typename T::value_type, const ucl_object_t *>>::type* = 0) -> void
@@ -436,7 +442,7 @@ auto sort_ucl_container_with_default(T &cont, const char *default_sort,
 		auto sort_view = std::string_view{real_sort};
 		auto inverse = false;
 
-		if (sort_view.ends_with(":asc")) {
+		if (sv_ends_with(sort_view, ":asc")) {
 			inverse = true;
 			sort_view = std::string_view{sort, strlen(sort) - sizeof(":asc") + 1};
 		}