Add -z undefs option to the ELF linker.

  Currently we have no obvious way to revert the action of the "-z defs"
  command line option.  The "--unresolved-symbols=ignore-in-object-files"
  does pretty much what is needed, but it is non-obvious and it also
  touches the setting for reporting unresolved symbol references from
  shared libraries.  So I am proposing adding a "-z undefs" option to be
  the inverse of "-z defs".  (I thought that "-z nodefs" might be
  confusing since it implies banning all definitions, rather than
  allowing them).

  In addition the description of the "-z defs" option in the linker
  documentation is misleading in one place, where it says:

    'defs'
       Disallows undefined symbols in object files.  Undefined
       symbols in shared libraries are still allowed.

  whereas later on it gets it right:

    '-z defs'
       Report unresolved symbol references from regular object files.
       This is done even if the linker is creating a non-symbolic shared
       library.  The switch '--[no-]allow-shlib-undefined' controls the
       behaviour for reporting unresolved references found in shared
       libraries being linked in.

	* emultempl/elf32.em (_handle_option): Add support for "-z undefs"
	as the opposite of "-z defs".
	* ld.texinfo: Document the new option.  Update the description of
	the -z defs option to make it clear that it does generate an error
	if an undefined symbol reference is found in an object file whilst
	creating a shared library.
	* NEWS: Document this new feature.

1 files changed, 2 insertions, 0 deletions

diff --git a/ld/emultempl/elf32.em b/ld/emultempl/elf32.em
index 8ff19bf..c0925fc 100644
--- a/ld/emultempl/elf32.em
+++ b/ld/emultempl/elf32.em
@@ -2726,6 +2726,8 @@ fragment <<EOF
     case 'z':
       if (strcmp (optarg, "defs") == 0)
 	link_info.unresolved_syms_in_objects = RM_GENERATE_ERROR;
+      else if (strcmp (optarg, "undefs") == 0)
+	link_info.unresolved_syms_in_objects = RM_IGNORE;
       else if (strcmp (optarg, "muldefs") == 0)
 	link_info.allow_multiple_definition = TRUE;
       else if (CONST_STRNEQ (optarg, "max-page-size="))