elf: Update comments for check_relocs in elf_backend_data

Since

commit 5c3261b0e8
Author: H.J. Lu <hjl.tools@gmail.com>
Date:   Mon Oct 16 03:49:54 2017 -0700

    ELF: Call check_relocs after opening all inputs

check_relocs is called after opening all inputs.

	* elf-bfd.h (elf_backend_data::check_relocs): Update comments.

bfd/elf-bfd.h

@@ -1088,13 +1088,11 @@ struct elf_backend_data
      that CHECK_RELOCS will properly process them.  PR 4424.  */
   bool (*relocs_compatible) (const bfd_target *, const bfd_target *);
 
-  /* The CHECK_RELOCS function is called by the add_symbols phase of
-     the ELF backend linker.  It is called once for each section with
-     relocs of an object file, just after the symbols for the object
-     file have been added to the global linker hash table.  The
-     function must look through the relocs and do any special handling
-     required.  This generally means allocating space in the global
-     offset table, and perhaps allocating space for a reloc.  The
+  /* The CHECK_RELOCS function is called after all input files have been
+     opened.  It is called once for each section with relocs of an object
+     file.  The function must look through the relocs and do any special
+     handling required.  This generally means allocating space in the
+     global offset table, and perhaps allocating space for a reloc.  The
      relocs are always passed as Rela structures; if the section
      actually uses Rel structures, the r_addend field will always be
      zero.  */