PR30592 objcopy: allow --set-section-flags to add or remove SHF_X86_64_LARGE

PR30592 objcopy: allow --set-section-flags to add or remove SHF_X86_64_LARGE

For example, objcopy --set-section-flags .data=alloc,large will add
SHF_X86_64_LARGE to the .data section.  Omitting "large" will drop the
SHF_X86_64_LARGE flag.

The bfd_section flag is named generically, SEC_ELF_LARGE, in case other
processors want to follow SHF_X86_64_LARGE.  SEC_ELF_LARGE has the same
value as SEC_TIC54X_BLOCK used by coff.

bfd/
    * section.c: Define SEC_ELF_LARGE.
    * bfd-in2.h: Regenerate.
    * elf64-x86-64.c (elf_x86_64_section_flags, elf_x86_64_fake_sections,
    elf_x86_64_copy_private_section_data): New.

binutils/
    * NEWS: Mention the new feature for objcopy.
    * doc/binutils.texi: Mention "large".
    * objcopy.c (parse_flags): Parse "large".
    (check_new_section_flags): Error if "large" is used with a
    non-x86-64 ELF target.
    * testsuite/binutils-all/x86-64/large-sections.d: New.
    * testsuite/binutils-all/x86-64/large-sections.s: New.
    * testsuite/binutils-all/x86-64/large-sections-i386.d: New.
    * testsuite/binutils-all/x86-64/large-sections-2.d: New.
    * testsuite/binutils-all/x86-64/large-sections-2-x32.d: New.