Add pe/x86_64 bigobj file format.

bfd/
	* peicode.h (pe_ILF_object_p): Adjust, as the version number
	has been read.
	(pe_bfd_object_p): Also read version number to detect ILF.
	* pe-x86_64.c (COFF_WITH_PE_BIGOBJ): Define.
	(x86_64pe_bigobj_vec): Define
	* coffcode.h (bfd_coff_backend_data): Add _bfd_coff_max_nscns field.
	(bfd_coff_max_nscns): New macro.
	(coff_compute_section_file_positions): Use unsigned int for
	target_index.  Compare with bfd_coff_max_nscns.
	(bfd_coff_std_swap_table, ticoff0_swap_table, ticoff1_swap_table):
	Set a value for _bfd_coff_max_nscns.
	(header_bigobj_classid): New constant.
	(coff_bigobj_swap_filehdr_in, coff_bigobj_swap_filehdr_out)
	(coff_bigobj_swap_sym_in, coff_bigobj_swap_sym_out)
	(coff_bigobj_swap_aux_in, coff_bigobj_swap_aux_out): New
	functions.
	(bigobj_swap_table): New table.
	* libcoff.h: Regenerate.
	* coff-sh.c (bfd_coff_small_swap_table): Likewise.
	* coff-alpha.c (alpha_ecoff_backend_data): Add value for
	_bfd_coff_max_nscns.
	* coff-mips.c (mips_ecoff_backend_data): Likewise.
	* coff-rs6000.c (bfd_xcoff_backend_data)
	(bfd_pmac_xcoff_backend_data): Likewise.
	* coff64-rs6000.c (bfd_xcoff_backend_data)
	(bfd_xcoff_aix5_backend_data): Likewise.
	* targets.c (x86_64pe_bigobj_vec): Declare.
	* configure.in (x86_64pe_bigobj_vec): New vector.
	* configure: Regenerate.
	* config.bfd: Add bigobj object format for Windows targets.

gas/
	* config/tc-i386.c (use_big_obj): Declare.
	(OPTION_MBIG_OBJ): Define.
	(md_longopts): Add -mbig-obj option.
	(md_parse_option): Handle it.
	(md_show_usage): Display help for this option.
	(i386_target_format): Use bigobj for x86-64 if -mbig-obj.
	* doc/c-i386.texi: Document the option.

gas/testsuite/
	* gas/pe/big-obj.d, gas/pe/big-obj.s: Add test.
	* gas/pe/pe.exp: Add test.

include/coff/
	* pe.h (struct external_ANON_OBJECT_HEADER_BIGOBJ): Declare.
	(FILHSZ_BIGOBJ): Define.
	(struct external_SYMBOL_EX): Declare.
	(SYMENT_BIGOBJ, SYMESZ_BIGOBJ): Define.
	(union external_AUX_SYMBOL_EX): Declare.
	(AUXENT_BIGOBJ, AUXESZ_BIGOBJ): Define.
	* internal.h (struct internal_filehdr): Change type
	of f_nscns.

include/coff/pe.h

@@ -358,6 +358,85 @@ typedef struct
 #define IMAGE_WEAK_EXTERN_SEARCH_LIBRARY	2
 #define IMAGE_WEAK_EXTERN_SEARCH_ALIAS		3
 
+/* Bigobj header.  */
+struct external_ANON_OBJECT_HEADER_BIGOBJ
+{
+  /* ANON_OBJECT_HEADER_V2 header.  */
+  char Sig1[2];
+  char Sig2[2];
+  char Version[2];
+  char Machine[2];
+  char TimeDateStamp[4];
+  char ClassID[16];
+  char SizeOfData[4];
+  char Flags[4];
+  char MetaDataSize[4];
+  char MetaDataOffset[4];
+
+  /* BIGOBJ specific.  */
+  char NumberOfSections[4];
+  char PointerToSymbolTable[4];
+  char NumberOfSymbols[4];
+};
+
+#define FILHSZ_BIGOBJ (14 * 4)
+
+struct external_SYMBOL_EX
+{
+  union
+  {
+    char e_name[E_SYMNMLEN];
+
+    struct
+    {
+      char e_zeroes[4];
+      char e_offset[4];
+    } e;
+  } e;
+
+  char e_value[4];
+  char e_scnum[4];
+  char e_type[2];
+  char e_sclass[1];
+  char e_numaux[1];
+} ATTRIBUTE_PACKED ;
+
+#define	SYMENT_BIGOBJ	struct external_SYMBOL_EX
+#define	SYMESZ_BIGOBJ	20
+
+#define FILNMLEN_BIGOBJ	20
+
+union external_AUX_SYMBOL_EX
+{
+  struct
+  {
+    char WeakDefaultSymIndex[4];
+    char WeakSearchType[4];
+    char rgbReserved[12];
+  } Sym;
+
+  struct
+  {
+    char Name[FILNMLEN_BIGOBJ];
+  } File;
+
+  struct
+  {
+    char Length[4];	/* section length */
+    char NumberOfRelocations[2];	/* # relocation entries */
+    char NumberOfLinenumbers[2];	/* # line numbers */
+    char Checksum[4];		   /* section COMDAT checksum	      */
+    char Number[2];	   /* COMDAT associated section index */
+    char Selection[1];		   /* COMDAT selection number	      */
+    char bReserved[1];
+    char HighNumber[2];           /* High bits of COMDAT associated sec.  */
+    char rgbReserved[2];
+  } Section;
+} ATTRIBUTE_PACKED;
+
+#define	AUXENT_BIGOBJ	union external_AUX_SYMBOL_EX
+#define	AUXESZ_BIGOBJ	20
+
 /* .pdata/.xdata defines and structures for x64 PE+ for exception handling.  */
 
 /* .pdata in exception directory.  */