[gold commit] Fix handling of __ehdr_start

[Cary Coutant]

I've backported this patch to the binutils-2.24 branch.

-cary

>     Fix handling of __ehdr_start when it cannot be defined.
>
>     2014-05-02  Cary Coutant  <ccoutant@google.com>
>
>         * defstd.cc (in_segment): Define __ehdr_start here...
>         * layout.cc (Layout::finalize): ...Instead of here.  Set the
>         output segment when known.
>         * resolve.cc (Symbol::override_base_with_special): Remember
>         the original binding.
>         * symtab.cc (Symbol::set_output_segment): New function.
>         (Symbol::set_undefined): New function.
>         * symtab.h (Symbol::is_weak_undefined): Check original undef
>         binding.
>         (Symbol::is_strong_undefined): New function.
>         (Symbol::set_output_segment): New function.
>         (Symbol::set_undefined): New function.
>         * target-reloc.h (is_strong_undefined): Remove.
>         (issue_undefined_symbol_error): Call Symbol::is_weak_undefined.
>         Check for hidden undefs.
>         (relocate_section): Call Symbol::is_strong_undefined.
>
>         * testsuite/Makefile.am (ehdr_start_test_1)
>         (ehdr_start_test_2, ehdr_start_test_3)
>         (ehdr_start_test_4, ehdr_start_test_5): New test cases.
>         * testsuite/Makefile.in: Regenerate.
>         * testsuite/ehdr_start_def.cc: New source file.
>         * testsuite/ehdr_start_test.cc: New source file.
>         * testsuite/ehdr_start_test.t: New linker script.
>         * testsuite/ehdr_start_test_4.sh: New shell script.