Revert "Revert "Ignore warning for instantiation after specialization.""

This reverts commit ee7a1c5d327e132c923cd45b5b2de091204f07dd.

Bug: http://b/31532493
Test: Manual validation
diff --git a/runtime/base/arena_allocator.cc b/runtime/base/arena_allocator.cc
index 61e0aab..1caf0c0 100644
--- a/runtime/base/arena_allocator.cc
+++ b/runtime/base/arena_allocator.cc
@@ -144,8 +144,11 @@
   }
 }
 
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Winstantiation-after-specialization"
 // Explicitly instantiate the used implementation.
 template class ArenaAllocatorStatsImpl<kArenaAllocatorCountAllocations>;
+#pragma GCC diagnostic pop
 
 void ArenaAllocatorMemoryTool::DoMakeDefined(void* ptr, size_t size) {
   MEMORY_TOOL_MAKE_DEFINED(ptr, size);