bfd: Fix build with -DDEBUG=2

When building with -DDEBUG=2, bfd doesn't compile:

In file included from bfd/elfcode.h:2051,
                 from bfd/elf32.c:23:
bfd/elfcore.h: In function ‘_bfd_elf32_core_find_build_id’:
bfd/elfcore.h:354:3: error: implicit declaration of function ‘elf_debug_file’; did you mean ‘elf_debug_section’? [-Wimplicit-function-declaration]
  354 |   elf_debug_file (&i_ehdr);
      |   ^~~~~~~~~~~~~~
      |   elf_debug_section

This happens because a guard in elfcore.h doesn't match the others.

This patch fixes this, allowing the build to complete.

Tested on amd64-pc-solaris2.11.

2025-09-15  Rainer Orth  <ro@CeBiTec.Uni-Bielefeld.DE>

	bfd:
	* elfcore.h [DEBUG]: Fix guard.