[vm] Avoid usage of STL container with const template argument

Issue b/223663984

TEST=ci

Change-Id: I7b915014df78641e4924cde2f07f9b55ee4bac7d
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/237583
Reviewed-by: Slava Egorov <vegorov@google.com>
Commit-Queue: Martin Kustermann <kustermann@google.com>
diff --git a/runtime/vm/os_fuchsia.cc b/runtime/vm/os_fuchsia.cc
index 448a10b..84bf154 100644
--- a/runtime/vm/os_fuchsia.cc
+++ b/runtime/vm/os_fuchsia.cc
@@ -294,7 +294,7 @@
 };
 
 // The timezone names encountered so far.  The timezone names must live forever.
-std::set<const std::string> timezone_names;
+std::set<std::string> timezone_names;
 
 // Initialized on OS:Init(), deinitialized on OS::Cleanup.
 std::shared_ptr<InspectMetrics> metrics;
@@ -460,9 +460,6 @@
   return -1;
 }
 
-// The timezone names encountered so far.  The timezone names must live forever.
-std::set<const std::string> timezone_names;
-
 // TODO(5411554):  May need to hoist these architecture dependent code
 // into a architecture specific file e.g: os_ia32_fuchsia.cc
 intptr_t OS::ActivationFrameAlignment() {