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.