warn unused result for bfd IO functions

This patch fixes all the warnings I found in bfd, binutils and ld,
plus some bitrotted COFF_GO32 code that tried to allocate -168ul
bytes.  When the malloc fail was reported these testsuite fails
resulted:

i386-go32  +FAIL: go32 stub
i386-go32  +ERROR: tcl error sourcing /home/alan/src/binutils-gdb/ld/testsuite/ld-i386/i386.exp.
i386-go32  +ERROR: couldn't open "tmpdir/go32stub": no such file or directory
i386-go32  +FAIL: ld-scripts/sane1
i386-go32  +FAIL: ld-scripts/assign-loc
i386-go32  +FAIL: ld-scripts/pr18963

This does result in some warnings in gdb which are fixed in a followup
patch.

bfd/
	* bfdio.c (bfd_read, bfd_write): Add ATTRIBUTE_WARN_UNUSED_RESULT.
	(bfd_tell, bfd_stat, bfd_seek, bfd_mmap): Likewise.
	* bfd-in2.h: Regenerate.
	* coff-rs6000.c (xcoff_write_armap_big) Don't ignore bfd_write
	return value.
	(xcoff_generate_rtinit): Likewise.  Also free data_buffer and
	string_table before returning.
	* coff64-rs6000.c (xcoff64_generate_rtinit): Likewise.
	* coff-stgo32.c (go32exe_check_format): Don't ignore bfd_seek
	return value.
	* coffcode.h (coff_apply_checksum): Don't ignore bfd_write return.
	(coff_write_object_contents <COFF_GO32>): Likewise, and bfd_malloc.
	Fix bitrotted code to look for first section with non-zero filepos.
	* elf64-ia64-vms.c (elf64_vms_write_shdrs_and_ehdr): Don't ignore
	bfd_seek or bfd_write return values.
	* pef.c (bfd_pef_scan_section): Likewise.
	(bfd_pef_read_header, bfd_pef_xlib_read_header): Likewise.
	* vms-misc.c (_bfd_vms_output_end): Likewise.  Return status.
	* vms.h (_bfd_vms_output_end): Update prototype.
	* vms-alpha.c: Pass _bfd_vms_output_end status up call chains.
	* wasm-module.c (wasm_compute_custom_section_file_position): Don't
	ignore bfd_seek or bfd_write return values.
	(wasm_compute_section_file_positions): Likewise.
	* xsym.c (bfd_sym_scan): Don't ignore bfd_seek return value.
	(bfd_sym_read_name_table): Likewise.
binutils/
	* ar.c (print_contents, extract_file): Don't ignore bfd_seek
	return value.
ld/
	* pdb.c (create_section_contrib_substream): Don't ignore bfd_seek
	return value.
	(create_section_header_stream): Likewise.
	* pe-dll.c (pe_get16, pe_get32): Add fail param to return results
	from bfd_seek and bfd_read.
	(pe_implied_import_dll): Handle these fails, and other bfd_seek
	and bfd_read return values.

ld/pe-dll.c

@@ -3419,22 +3419,30 @@ pe_process_import_defs (bfd *output_bfd, struct bfd_link_info *linfo)
    handled, FALSE if not.  */
 
 static unsigned int
-pe_get16 (bfd *abfd, int where)
+pe_get16 (bfd *abfd, int where, bool *fail)
 {
   unsigned char b[2];
 
-  bfd_seek (abfd, where, SEEK_SET);
-  bfd_read (b, 2, abfd);
+  if (bfd_seek (abfd, where, SEEK_SET) != 0
+      || bfd_read (b, 2, abfd) != 2)
+    {
+      *fail = true;
+      return 0;
+    }
   return b[0] + (b[1] << 8);
 }
 
 static unsigned int
-pe_get32 (bfd *abfd, int where)
+pe_get32 (bfd *abfd, int where, bool *fail)
 {
   unsigned char b[4];
 
-  bfd_seek (abfd, where, SEEK_SET);
-  bfd_read (b, 4, abfd);
+  if (bfd_seek (abfd, where, SEEK_SET) != 0
+      || bfd_read (b, 4, abfd) != 4)
+    {
+      *fail = true;
+      return 0;
+    }
   return b[0] + (b[1] << 8) + (b[2] << 16) + ((unsigned) b[3] << 24);
 }
 
@@ -3481,38 +3489,49 @@ pe_implied_import_dll (const char *filename)
   /* PEI dlls seem to be bfd_objects.  */
   if (!bfd_check_format (dll, bfd_object))
     {
+    notdll:
       einfo (_("%X%P: %s: this doesn't appear to be a DLL\n"), filename);
       return false;
     }
 
   /* Get pe_header, optional header and numbers of directory entries.  */
-  pe_header_offset = pe_get32 (dll, 0x3c);
+  bool fail = false;
+  pe_header_offset = pe_get32 (dll, 0x3c, &fail);
+  if (fail)
+    goto notdll;
   opthdr_ofs = pe_header_offset + 4 + 20;
 #ifdef pe_use_plus
-  num_entries = pe_get32 (dll, opthdr_ofs + 92 + 4 * 4); /*  & NumberOfRvaAndSizes.  */
+  /* NumberOfRvaAndSizes.  */
+  num_entries = pe_get32 (dll, opthdr_ofs + 92 + 4 * 4, &fail);
 #else
-  num_entries = pe_get32 (dll, opthdr_ofs + 92);
+  num_entries = pe_get32 (dll, opthdr_ofs + 92, &fail);
 #endif
+  if (fail)
+    goto notdll;
 
   /* No import or export directory entry.  */
   if (num_entries < 1)
     return false;
 
 #ifdef pe_use_plus
-  export_rva  = pe_get32 (dll, opthdr_ofs + 96 + 4 * 4);
-  export_size = pe_get32 (dll, opthdr_ofs + 100 + 4 * 4);
+  export_rva  = pe_get32 (dll, opthdr_ofs + 96 + 4 * 4, &fail);
+  export_size = pe_get32 (dll, opthdr_ofs + 100 + 4 * 4, &fail);
 #else
-  export_rva = pe_get32 (dll, opthdr_ofs + 96);
-  export_size = pe_get32 (dll, opthdr_ofs + 100);
+  export_rva = pe_get32 (dll, opthdr_ofs + 96, &fail);
+  export_size = pe_get32 (dll, opthdr_ofs + 100, &fail);
 #endif
+  if (fail)
+    goto notdll;
 
   /* No export table - nothing to export.  */
   if (export_size == 0)
     return false;
 
-  nsections = pe_get16 (dll, pe_header_offset + 4 + 2);
+  nsections = pe_get16 (dll, pe_header_offset + 4 + 2, &fail);
   secptr = (pe_header_offset + 4 + 20 +
-	    pe_get16 (dll, pe_header_offset + 4 + 16));
+	    pe_get16 (dll, pe_header_offset + 4 + 16, &fail));
+  if (fail)
+    goto notdll;
   expptr = 0;
 
   /* Get the rva and size of the export section.  */
@@ -3520,12 +3539,14 @@ pe_implied_import_dll (const char *filename)
     {
       char sname[8];
       bfd_vma secptr1 = secptr + 40 * i;
-      bfd_vma vaddr = pe_get32 (dll, secptr1 + 12);
-      bfd_vma vsize = pe_get32 (dll, secptr1 + 16);
-      bfd_vma fptr = pe_get32 (dll, secptr1 + 20);
+      bfd_vma vaddr = pe_get32 (dll, secptr1 + 12, &fail);
+      bfd_vma vsize = pe_get32 (dll, secptr1 + 16, &fail);
+      bfd_vma fptr = pe_get32 (dll, secptr1 + 20, &fail);
 
-      bfd_seek (dll, secptr1, SEEK_SET);
-      bfd_read (sname, 8, dll);
+      if (fail
+	  || bfd_seek (dll, secptr1, SEEK_SET) != 0
+	  || bfd_read (sname, 8, dll) != 8)
+	goto notdll;
 
       if (vaddr <= export_rva && vaddr + vsize > export_rva)
 	{
@@ -3541,14 +3562,16 @@ pe_implied_import_dll (const char *filename)
   for (i = 0; i < nsections; i++)
     {
       bfd_vma secptr1 = secptr + 40 * i;
-      bfd_vma vsize = pe_get32 (dll, secptr1 + 8);
-      bfd_vma vaddr = pe_get32 (dll, secptr1 + 12);
-      bfd_vma flags = pe_get32 (dll, secptr1 + 36);
+      bfd_vma vsize = pe_get32 (dll, secptr1 + 8, &fail);
+      bfd_vma vaddr = pe_get32 (dll, secptr1 + 12, &fail);
+      bfd_vma flags = pe_get32 (dll, secptr1 + 36, &fail);
       char sec_name[9];
 
       sec_name[8] = '\0';
-      bfd_seek (dll, secptr1 + 0, SEEK_SET);
-      bfd_read (sec_name, 8, dll);
+      if (fail
+	  || bfd_seek (dll, secptr1 + 0, SEEK_SET) != 0
+	  || bfd_read (sec_name, 8, dll) != 8)
+	goto notdll;
 
       if (strcmp(sec_name,".data") == 0)
 	{
@@ -3583,8 +3606,9 @@ pe_implied_import_dll (const char *filename)
     }
 
   expdata = xmalloc (export_size);
-  bfd_seek (dll, expptr, SEEK_SET);
-  bfd_read (expdata, export_size, dll);
+  if (bfd_seek (dll, expptr, SEEK_SET) != 0
+      || bfd_read (expdata, export_size, dll) != export_size)
+    goto notdll;
   erva = (char *) expdata - export_rva;
 
   if (pe_def_file == 0)