Fix implicit conversion warning produced by clang

  When compiling with clang, which is part of Xcode 7.3, following warnings
are emitted:
objcopy.c:224:50: error: implicit conversion from enumeration type 'enum bfd_link_elf_stt_common' to different enumeration type 'enum bfd_link_discard' [-Werror,-Wenum-conversion]
static enum bfd_link_discard do_elf_stt_common = unchanged;
                             ~~~~~~~~~~~~~~~~~   ^~~~~~~~~
objcopy.c:4290:26: error: implicit conversion from enumeration type 'enum bfd_link_elf_stt_common' to different enumeration type 'enum bfd_link_discard' [-Werror,-Wenum-conversion]
            do_elf_stt_common = elf_stt_common;
                              ~ ^~~~~~~~~~~~~~
objcopy.c:4292:26: error: implicit conversion from enumeration type 'enum bfd_link_elf_stt_common' to different enumeration type 'enum bfd_link_discard' [-Werror,-Wenum-conversion]
            do_elf_stt_common = no_elf_stt_common;
                              ~ ^~~~~~~~~~~~~~~~~
3 errors generated.

This is risky, since essentially there is a coupling between 2 different
enum orderings. Also since by default warnings are promoted to errors
it breaks default build.

To reproduce: ./configure && make
Verified by: ./configure && make # above warnings disappear
---
 binutils/ChangeLog | 4 ++++
 binutils/objcopy.c | 2 +-
 2 files changed, 5 insertions(+), 1 deletion(-)
  

On Tuesday, June 14, 2016 10:55:42 AM Taras Tsugrii wrote:
> When compiling with clang, which is part of Xcode 7.3, following warnings
> are emitted:
> objcopy.c:224:50: error: implicit conversion from enumeration type 'enum bfd_link_elf_stt_common' to different enumeration type 'enum bfd_link_discard' [-Werror,-Wenum-conversion]
> static enum bfd_link_discard do_elf_stt_common = unchanged;
>                              ~~~~~~~~~~~~~~~~~   ^~~~~~~~~
> objcopy.c:4290:26: error: implicit conversion from enumeration type 'enum bfd_link_elf_stt_common' to different enumeration type 'enum bfd_link_discard' [-Werror,-Wenum-conversion]
>             do_elf_stt_common = elf_stt_common;
>                               ~ ^~~~~~~~~~~~~~
> objcopy.c:4292:26: error: implicit conversion from enumeration type 'enum bfd_link_elf_stt_common' to different enumeration type 'enum bfd_link_discard' [-Werror,-Wenum-conversion]
>             do_elf_stt_common = no_elf_stt_common;
>                               ~ ^~~~~~~~~~~~~~~~~
> 3 errors generated.
> 
> This is risky, since essentially there is a coupling between 2 different
> enum orderings. Also since by default warnings are promoted to errors
> it breaks default build.

I had the same patch in queue and just pushed it.  I have a few more patches
from clang warnings pending as well.  (I am testing with clang 3.8.0 in
FreeBSD.)  Some of clang's warnings are a bit noisy though and I haven't tried
to address the -Wunused-function spam from VEC() (I presume that GDB will
eventually switch the VEC stuff to templates which will fix that).  Also,
Some of the -Wtautological-compare warnings for things that do:

	if (foo >= 0 && foo <= bar)

where 'foo' is unsigned I haven't posted patches to "fix" as I'm not sure that
the existing code isn't more readable in its current form.
  

On 06/14/2016 08:07 PM, John Baldwin wrote:
> Some of clang's warnings are a bit noisy though and I haven't tried
> to address the -Wunused-function spam from VEC()

For the VEC spam, see:

 https://llvm.org/bugs/show_bug.cgi?id=22712

Thanks,
Pedro Alves
  

Hi Taras,
Thanks for the patch, but it should be sent to binutils@sourceware.org
mail list,
instead of gdb's.

On Tue, Jun 14, 2016 at 6:55 PM, Taras Tsugrii <ttsugrii@fb.com> wrote:
> diff --git a/binutils/ChangeLog b/binutils/ChangeLog
> index ff8161a..08be889 100644
> --- a/binutils/ChangeLog
> +++ b/binutils/ChangeLog
> @@ -1,3 +1,7 @@
> +2016-06-14  Taras Tsugrii  <taras.tsugriy@gmail.com>
> +
> +       * objcopy.c: Fix clang implicit conversion warning.
> +

ChangeLog entry describes "what is your change" rather than "why do you
change".