Use DIAGNOSTIC_IGNORE_STRINGOP_TRUNCATION to silence GCC 8.1

Use DIAGNOSTIC_IGNORE_STRINGOP_TRUNCATION to silence GCC 8.1

GCC 8.1 warns about destination size with -Wstringop-truncation:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85643

Use DIAGNOSTIC_IGNORE_STRINGOP_TRUNCATION to silence it.

bfd/

	PR binutils/23146
	* bfd-in.h: Include "diagnostics.h".
	* bfd-in2.h: Regenerated.
	* elf32-arm.c (elf32_arm_nabi_write_core_note): Use
	DIAGNOSTIC_PUSH, DIAGNOSTIC_IGNORE_STRINGOP_TRUNCATION and
	DIAGNOSTIC_POP to silence GCC 8.1 warnings with
	-Wstringop-truncation.
	* elf32-ppc.c (ppc_elf_write_core_note): Likewse.
	* elf32-s390.c (elf_s390_write_core_note): Likewse.
	* elf64-ppc.c (ppc64_elf_write_core_note): Likewse.
	* elf64-s390.c (elf_s390_write_core_note): Likewse.
	* elfxx-aarch64.c (_bfd_aarch64_elf_write_core_note): Likewse.

include/

	* diagnostics.h (DIAGNOSTIC_IGNORE_STRINGOP_TRUNCATION): Always
	define for GCC.