Simplify Garbage_collection::add_reference a bit.

this->section_reloc_map_[src_id] is created if it doesn't exist, so there
is no point in doing a find.

gold/ChangeLog

@@ -1,3 +1,7 @@
+2015-02-17  Rafael Ávila de Espíndola <rafael.espindola@gmail.com>
+
+	* gc.h (Garbage_collection::add_reference): Don't use find.
+
 2015-02-17  Rafael Ávila de Espíndola <rafael.espindola@gmail.com>
 
 	* object.cc (write_local_symbols): avoid std::vector copy.

gold/gc.h

@@ -109,11 +109,8 @@ class Garbage_collection
   {
     Section_id src_id(src_object, src_shndx);
     Section_id dst_id(dst_object, dst_shndx);
-    Section_ref::iterator p = this->section_reloc_map_.find(src_id);
-    if (p == this->section_reloc_map_.end())
-      this->section_reloc_map_[src_id].insert(dst_id);
-    else
-      p->second.insert(dst_id);
+    Sections_reachable& reachable = this->section_reloc_map_[src_id];
+    reachable.insert(dst_id);
   }
 
  private: