Use gdb unordered map in ravenscar.c

This changes ravenscar.c to use gdb::unordered_map.

Approved-By: Simon Marchi <simon.marchi@efficios.com>
diff --git a/gdb/ravenscar-thread.c b/gdb/ravenscar-thread.c
index 47db72b..dae6917 100644
--- a/gdb/ravenscar-thread.c
+++ b/gdb/ravenscar-thread.c
@@ -30,7 +30,7 @@
 #include "top.h"
 #include "regcache.h"
 #include "objfiles.h"
-#include <unordered_map>
+#include "gdbsupport/unordered_map.h"
 
 /* This module provides support for "Ravenscar" tasks (Ada) when
    debugging on bare-metal targets.
@@ -194,7 +194,7 @@ struct ravenscar_thread_target final : public target_ops
      needed because sometimes the runtime will report an active task
      that hasn't yet been put on the list of tasks that is read by
      ada-tasks.c.  */
-  std::unordered_map<ULONGEST, int> m_cpu_map;
+  gdb::unordered_map<ULONGEST, int> m_cpu_map;
 };
 
 /* Return true iff PTID corresponds to a ravenscar task.  */