[binutils-gdb] gdb: use gdb:hash_enum as hash function in offset_map_type

[gdb-buildbot@sergiodj.net]

*** TEST RESULTS FOR COMMIT 1b95cdb76caca1b7a9ecf9324acf23139f11f7d1 ***

commit 1b95cdb76caca1b7a9ecf9324acf23139f11f7d1
Author:     Simon Marchi <simon.marchi@efficios.com>
AuthorDate: Tue Apr 28 09:49:58 2020 -0400
Commit:     Simon Marchi <simon.marchi@efficios.com>
CommitDate: Tue Apr 28 09:50:12 2020 -0400

    gdb: use gdb:hash_enum as hash function in offset_map_type
    
    When building with g++ 4.8, we get this error (just an excerpt, because
    g++ outputs a very long error message):
    
          CXX    dwarf2/read.o
        ...
        /home/smarchi/src/binutils-gdb/gdb/dwarf2/read.c:14616:31:   required from here
        /usr/include/c++/4.8/bits/hashtable_policy.h:1070:12: error: invalid use of incomplete type struct std::hash<sect_offset>
             struct _Hash_code_base<_Key, _Value, _ExtractKey, _H1, _H2,
    
    This is the same problem and fix as in commit f23f598e28ad ("[gdb] Fix
    build breaker with gcc 4.8").  Pass an explicit hash function rather
    than relying on the default std::hash<sect_offset>.
    
    gdb/ChangeLog:
    
            PR gdb/25881
            * dwarf2/read.c (offset_map_type): Use
            gdb:hash_enum<sect_offset> as hash function.

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 76f6cf7896..f7931c23c6 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,9 @@
+2020-04-28  Simon Marchi  <simon.marchi@efficios.com>
+
+	PR gdb/25881
+	* dwarf2/read.c (offset_map_type): Use
+	gdb:hash_enum<sect_offset> as hash function.
+
 2020-04-28  Tom de Vries  <tdevries@suse.de>
 
 	* dwarf2/read.c (process_structure_scope): Add symbol for struct decl
diff --git a/gdb/dwarf2/read.c b/gdb/dwarf2/read.c
index 82564edd7b..c5528887fa 100644
--- a/gdb/dwarf2/read.c
+++ b/gdb/dwarf2/read.c
@@ -14513,7 +14513,8 @@ dwarf2_add_type_defn (struct field_info *fip, struct die_info *die,
 
 /* A convenience typedef that's used when finding the discriminant
    field for a variant part.  */
-typedef std::unordered_map<sect_offset, int> offset_map_type;
+typedef std::unordered_map<sect_offset, int, gdb::hash_enum<sect_offset>>
+  offset_map_type;
 
 /* Compute the discriminant range for a given variant.  OBSTACK is
    where the results will be stored.  VARIANT is the variant to