PR 28447: implement multiple parameters for .file on XCOFF

On XCOFF, ".file" pseudo-op allows 3 extras parameters to provide
additional information to AIX linker, or its debugger. These are
stored in auxiliary entries of the C_FILE symbol.

bfd/
	PR 28447
	* coffcode.h (combined_entry_type): Add extrap field.
	(coff_bigobj_swap_aux_in): Adjust names of x_file fields.
	(coff_bigobj_swap_aux_out): Likewise.
	* coffgen.c (coff_write_auxent_fname): New function.
	(coff_fix_symbol_name): Write x_file using
	 coff_write_auxent_fname.
	(coff_write_symbol): Likewise.
	(coff_write_symbols): Add C_FILE auxiliary entries to
	string table if needed.
	(coff_get_normalized_symtab): Adjust names of x_file fields.
	Normalize C_FILE auxiliary entries.
	(coff_print_symbol): Print C_FILE auxiliary entries.
	* coff-rs6000.c (_bfd_xcoff_swap_aux_in): Adjust names of
	x_file fields.
	(_bfd_xcoff_swap_aux_out): Likewise.
	* coff64-rs6000.c (_bfd_xcoff64_swap_aux_in): Likewise.
	(_bfd_xcoff64_swap_aux_out): Likewise.
	* cofflink.c (_bfd_coff_final_link): Likewise.
	(_bfd_coff_link_input_bfd): Likewise.
	* coffswap.h (coff_swap_aux_in): Likewise.
	* peXXigen.c (_bfd_XXi_swap_aux_in): Likewise.
	(_bfd_XXi_swap_aux_out): Likewise.
	* xcofflink.c (xcoff_link_input_bfd): Likewise.
	* libcoff.h: Regenerate.
gas/
	* config/tc-ppc.c (ppc_file): New function.
	* config/tc-ppc.h (OBJ_COFF_MAX_AUXENTRIES): Change to 4.
	* testsuite/gas/ppc/aix.exp: Add tests.
	* testsuite/gas/ppc/xcoff-file-32.d: New test.
	* testsuite/gas/ppc/xcoff-file-64.d: New test.
	* testsuite/gas/ppc/xcoff-file.s: New test.
include/
	* coff/internal.h (union internal_auxent): Change x_file to be a
	  struct instead of a union. Add x_ftype field.
	* coff/rs6000.h (union external_auxent): Add x_resv field.
	* coff/xcoff.h (XFT_FN): New define.
	(XFT_CT): Likewise.
	(XFT_CV): Likewise.
	(XFT_CD): Likewise.