GC: Also check the local debug definition section
    
    Extend
    
    commit b7c871edcd83ccdc5fcd8148a7f433efd6b52255
    Author: H.J. Lu <hjl.tools@gmail.com>
    Date:   Wed May 17 07:57:15 2017 -0700
    
        Mark debug sections referenced by kept debug sections
    
    to handle the local debug definition section.
    
    bfd/
    
    	PR ld/20882
    	* elflink.c (elf_gc_mark_debug_section): Also check the local
    	debug definition section.
    
    ld/
    
    	PR ld/20882
    	* testsuite/ld-gc/pr20882.d: Also dump and check .debug_abbrev
    	section.
    	* testsuite/ld-gc/pr20882b.s: Add .debug_abbrev section.
    
    (cherry picked from commit 9e223787a474c672c5f1cfd4574857241ae4eafa)