The libc++ upgrade means we can use contains() in the linker now.

Change-Id: I30f764ddfd101dde1b7bbcefbf78182a19b3db7c
diff --git a/linker/linker.cpp b/linker/linker.cpp
index 8b467a3..e13d37d 100644
--- a/linker/linker.cpp
+++ b/linker/linker.cpp
@@ -3595,7 +3595,7 @@
   // 2. Initialize other namespaces
 
   for (auto& ns_config : namespace_configs) {
-    if (namespaces.find(ns_config->name()) != namespaces.end()) {
+    if (namespaces.contains(ns_config->name())) {
       continue;
     }