Always keep sections marked with SEC_KEEP

Always keep sections marked with SEC_KEEP

SEC_KEEP check in elf_gc_sweep was missing in commit:

commit bde6f3eb6dff94cea1d471e15c6154d55d49820f
Author: H.J. Lu <hjl.tools@gmail.com>
Date:   Fri Jan 8 01:43:23 2010 +0000

    Set SEC_KEEP on section XXX for undefined __start_XXX/__stop_XXX

    bfd/

    2010-01-07  H.J. Lu  <hongjiu.lu@intel.com>

      PR ld/11133
      * elflink.c (_bfd_elf_gc_mark_hook): Check section XXX for
      undefined __start_XXX/__stop_XXX in all input files and set
      SEC_KEEP.

This patch adds SEC_KEEP check to elf_gc_sweep.

bfd/

	PR ld/19161
	* elflink.c (elf_gc_sweep): Always keep sections marked with
	SEC_KEEP.

ld/testsuite/

	PR ld/19161
	* ld-gc/gc.exp: Run pr19161 test.
	* ld-gc/pr19161-1.c: New file.
	* ld-gc/pr19161-2.c: Likewise.
	* ld-gc/pr19161.d: Likewise.