[AArch64] Skip IFUNC relocations in debug sections
    
    Skip IFUNC relocations in debug sections ignored by ld.so.
    Fixes the following ld test failures on aarch64:
    
    FAIL: Build libpr18808.so
    FAIL: Build libpr18808.so_2
    FAIL: Run pr18808
    
    aborting at bfd/elfnn-aarch64.c:4986 in elf64_aarch64_final_link_relocate.
    
    bfd/
    	PR ld/18808
    	* elfnn-aarch64.c (elfNN_aarch64_final_link_relocate): Skip IFUNC
    	relocations in debug sections, change abort to _bfd_error_handler.