Don't build ld.so with -Wl,-z,now

Don't build ld.so with -Wl,-z,now

PLT entries aren't required when -z now used.  Linker on master with:

commit 25070364b0ce33eed46aa5d78ebebbec6accec7e
Author: H.J. Lu <hjl.tools@gmail.com>
Date:   Sat May 16 07:00:21 2015 -0700

    Don't generate PLT relocations for now binding

    There is no need for PLT relocations with -z now. We can use GOT
    relocations, which take less space, instead and replace 16-byte .plt
    entres with 8-byte .plt.got entries.

    bfd/

      * elf32-i386.c (elf_i386_check_relocs): Create .plt.got section
      for now binding.
      (elf_i386_allocate_dynrelocs): Use .plt.got section for now
      binding.
      * elf64-x86-64.c (elf_x86_64_check_relocs): Create .plt.got
      section for now binding.
      (elf_x86_64_allocate_dynrelocs): Use .plt.got section for now
      binding.

won't generate PLT entries with -z now.  elf/tst-audit2.c has

/* This calloc definition will be called by the dynamic linker itself.
   We test that it has initialized our TLS block by the time it does so.
*/

void *
calloc (size_t n, size_t m)
{
  if (magic[0] != MAGIC1 || magic[1] != MAGIC2)
    {
      printf ("{%x, %x} != {%x, %x}\n", magic[0], magic[1], MAGIC1, MAGIC2);
      abort ();
    }
  magic[0] = MAGIC2;
  magic[1] = MAGIC1;

Since ld.so is built with -z now, there are no PLT relocations and this
calloc won't be used:

Relocation section '.rela.dyn' at offset 0x66c contains 16 entries:
 Offset     Info    Type            Sym.Value  Sym. Name + Addend
00222e88  00000008 R_X86_64_RELATIVE            10970
00222e8c  00000008 R_X86_64_RELATIVE            f8f0
00222e90  00000008 R_X86_64_RELATIVE            f6c0
00222e94  00000008 R_X86_64_RELATIVE            11bd0
00222e98  00000008 R_X86_64_RELATIVE            a1b0
00222e9c  00000008 R_X86_64_RELATIVE            130c0
00222ea0  00000008 R_X86_64_RELATIVE            13c50
00222ea4  00000008 R_X86_64_RELATIVE            15fc0
00222ea8  00000008 R_X86_64_RELATIVE            12cd0
00222eac  00000008 R_X86_64_RELATIVE            17f90
00222fbc  00000a06 R_X86_64_GLOB_DAT 00018230	__libc_memalign@@GLIBC_2.16 + 0
00222fc4  00001506 R_X86_64_GLOB_DAT 00018300   malloc@@GLIBC_2.16 + 0
00222fcc  00000d06 R_X86_64_GLOB_DAT 00018310   calloc@@GLIBC_2.16 + 0
00222fd4  00000506 R_X86_64_GLOB_DAT 000184a0   realloc@@GLIBC_2.16 + 0
00222fdc  00000706 R_X86_64_GLOB_DAT 002239a0   _r_debug@@GLIBC_2.16 + 0
00222fe4  00000406 R_X86_64_GLOB_DAT 00018340   free@@GLIBC_2.16 + 0

Assuming we do want to keep PLT relocations in ld.so so that malloc
functions in ld.so can be overridden, ld.so should be built with -z now.
There is no reason to build ld.so with -z now since ld.so is the one
doing BIND_NOW.  The only thing we get with -z now on ld.so is DT tag:

 0x0000000000000018 (BIND_NOW)
 0x000000006ffffffb (FLAGS_1)            Flags: NOW

This patch removes -Wl,-z,now from ld.so build.

	[BZ #18422]
	* elf/Makefile (z-now-yes): Removed.
	($(objpfx)ld.so): Remove $(z-now-$(bind-now)).