Use addrmap_fixed in a few spots

There are a few spots in the tree that use 'addrmap' where only an
addrmap_fixed will ever really be seen.  This patch changes this code
to use the more specific type.

gdb/block.h

@@ -30,7 +30,7 @@ struct compunit_symtab;
 struct block_namespace_info;
 struct using_direct;
 struct obstack;
-struct addrmap;
+struct addrmap_fixed;
 
 /* Blocks can occupy non-contiguous address ranges.  When this occurs,
    startaddr and endaddr within struct block (still) specify the lowest
@@ -410,22 +410,22 @@ struct blockvector
   { return this->block (STATIC_BLOCK); }
 
   /* Return the address -> block map of this blockvector.  */
-  addrmap *map ()
+  addrmap_fixed *map ()
   { return m_map; }
 
   /* Const version of the above.  */
-  const addrmap *map () const
+  const addrmap_fixed *map () const
   { return m_map; }
 
   /* Set this blockvector's address -> block map.  */
-  void set_map (addrmap *map)
+  void set_map (addrmap_fixed *map)
   { m_map = map; }
 
 private:
   /* An address map mapping addresses to blocks in this blockvector.
      This pointer is zero if the blocks' start and end addresses are
      enough.  */
-  struct addrmap *m_map;
+  addrmap_fixed *m_map;
 
   /* Number of blocks in the list.  */
   int m_num_blocks;

gdb/dwarf2/cooked-index.h

@@ -362,7 +362,7 @@ private:
   cooked_index_entry *m_main = nullptr;
   /* The addrmap.  This maps address ranges to dwarf2_per_cu_data
      objects.  */
-  addrmap *m_addrmap = nullptr;
+  addrmap_fixed *m_addrmap = nullptr;
   /* Storage for canonical names.  */
   std::vector<gdb::unique_xmalloc_ptr<char>> m_names;
 };

gdb/dwarf2/read.h

@@ -536,7 +536,7 @@ public:
     abstract_to_concrete;
 
   /* The address map that is used by the DWARF index code.  */
-  struct addrmap *index_addrmap = nullptr;
+  addrmap_fixed *index_addrmap = nullptr;
 };
 
 /* An iterator for all_units that is based on index.  This