bfd: don't produce corrupt COFF symbol table due to long ELF file name symbols

The re-writing logic in _bfd_coff_final_link() overwrote the ".file"
part of the symbol table entry, due to not coping with the auxiliary
entry generated in all cases.

Note that while I would have wanted to add a test case,
(a) I didn't spot any one testing the base functionality here, and
(b) I wasn't able to figure out proper conditionals to use in e.g.
    ld-elf/elf.exp to check for the necessary PE/PE+ support (which
    varies by target).

bfd/coffgen.c

@@ -1066,6 +1066,7 @@ bfd_boolean
 coff_write_alien_symbol (bfd *abfd,
 			 asymbol *symbol,
 			 struct internal_syment *isym,
+			 union internal_auxent *iaux,
 			 bfd_vma *written,
 			 bfd_size_type *string_size_p,
 			 asection **debug_string_section_p,
@@ -1151,6 +1152,8 @@ coff_write_alien_symbol (bfd *abfd,
 			   debug_string_section_p, debug_string_size_p);
   if (isym != NULL)
     *isym = native->u.syment;
+  if (iaux != NULL && native->u.syment.n_numaux)
+    *iaux = native[1].u.auxent;
   return ret;
 }
 
@@ -1268,7 +1271,7 @@ coff_write_symbols (bfd *abfd)
       if (c_symbol == (coff_symbol_type *) NULL
 	  || c_symbol->native == (combined_entry_type *) NULL)
 	{
-	  if (!coff_write_alien_symbol (abfd, symbol, NULL, &written,
+	  if (!coff_write_alien_symbol (abfd, symbol, NULL, NULL, &written,
 					&string_size, &debug_string_section,
 					&debug_string_size))
 	    return FALSE;