Backport .init_array/.fini_array work.

Android requires ".init_array" and ".fini_array" for
X86/MIPS as well, regardless the gcc version.  This
patch is basing on following patches:

commit d6b43a31
Author: Rafael Espindola <rafael.espindola@gmail.com>
Date:   Tue Jun 19 00:48:28 2012 +0000

  Move the support for using .init_array from ARM to the generic
  TargetLoweringObjectFileELF. Use this to support it on X86. Unlike ARM,
  on X86 it is not easy to find out if .init_array should be used or not, so
  the decision is made via TargetOptions and defaults to off.

  Add a command line option to llc that enables it.

commit 8af669f2f1d92436fe6dc43144bb084a620e7516
Author: Rafael Espindola <rafael.espindola@gmail.com>
Date:   Tue Jun 19 01:26:10 2012 +0000

  Add a -fuse-init-array option to cc1 and map to the UseInitArray target
  option. On the driver, check if we are using libraries from gcc 4.7 or newer
  and if so pass -fuse-init-array to the frontend.
  The crtbegin*.o files in gcc 4.7 no longer call the constructors listed in
  .ctors, so we have to use .init_array.