[PATCH][gdb] Fix build breaker with gcc 4.8

[Steve Ellcey]

On Wed, 2019-06-19 at 13:04 +0200, Tom de Vries wrote:
> 
> [gdb] Fix build breaker with gcc 4.8
> 
> gdb/ChangeLog:
> 
> 2019-06-19  Tom de Vries  <tdevries@suse.de>
> 
> 	* dwarf2read.h (std::hash<sect_offset>): New specialization.

I think this might have broken the GDB build with GCC 5.4.  My
gdb/binutils build using the latest sources is dying with the
following message.  I am building on Ubuntu 18.04 and the installed GCC
5.4 compiler.  I haven't seen any errors from the buildbot, maybe that
is using GCC 4.8?

Error:


In file included from /usr/include/c++/5/bits/hashtable.h:35:0,
                 from /usr/include/c++/5/unordered_map:47,
                 from /home/sellcey/tot/src/binutils-
gdb/gdb/dwarf2read.h:23,
                 from /home/sellcey/tot/src/binutils-gdb/gdb/dwarf-
index-write.h:24,
                 from /home/sellcey/tot/src/binutils-gdb/gdb/dwarf-
index-cache.c:28:
/usr/include/c++/5/bits/hashtable_policy.h: In instantiation of ‘struct
std::__detail::__is_noexcept_hash<sect_offset, std::hash<sect_offset>
>’:
/usr/include/c++/5/type_traits:137:12:   required from ‘struct
std::__and_<std::__is_fast_hash<std::hash<sect_offset> >,
std::__detail::__is_noexcept_hash<sect_offset, std::hash<sect_offset> >
>’
/usr/include/c++/5/type_traits:148:38:   required from ‘struct
std::__not_<std::__and_<std::__is_fast_hash<std::hash<sect_offset> >,
std::__detail::__is_noexcept_hash<sect_offset, std::hash<sect_offset> >
> >’

(etc, etc, etc)