Created attachment 6422 [details]
Broken fix attempt.

$ ./gdb /lib64/libc.so.6
GNU gdb (GDB) 7.4.50.20120523-cvs
(gdb) p memmove
$1 = {<text gnu-indirect-function variable, no debug info>} 0x88a70 <memmove>
(gdb) p memmove
$2 = {void *(void)} 0x88a70 <memmove>

DWARF has no way how to mark a function as IFUNC.  Only ELF has a way.
No DWARF DIE definition must use ELF IFUNC symbol names as GDB prefers DWARF symbols more than ELF symbols.

These DWARF DW_AT_linkage_name symbols are marked in ELF as IFUNC:
  __GI___strcasecmp __GI_time __gettimeofday __memmove_chk __sched_cpucount
  __strcasestr memmove strstr time

Out of those only these are of concern to users:
  memmove strstr time

 <0><18c0c5>: Abbrev Number: 1 (DW_TAG_compile_unit)
    <18c0cb>   DW_AT_name        : ../sysdeps/x86_64/multiarch/memmove.c
 <1><18c3f8>: Abbrev Number: 27 (DW_TAG_subprogram)
    <18c3f9>   DW_AT_external    : 1
    <18c3f9>   DW_AT_name        : memmove_ifunc
    <18c3fd>   DW_AT_decl_file   : 2
    <18c3fe>   DW_AT_decl_line   : 46
    <18c3ff>   DW_AT_linkage_name: memmove
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^
    <18c403>   DW_AT_prototyped  : 1
    <18c403>   DW_AT_type        : <0x18c126>
    <18c407>   DW_AT_low_pc      : 0x88a70
    <18c40f>   DW_AT_high_pc     : 0x88ab7
    <18c417>   DW_AT_frame_base  : 1 byte block: 9c     (DW_OP_call_frame_cfa)
    <18c419>   DW_AT_GNU_all_call_sites: 1
    <18c419>   DW_AT_sibling     : <0x18c43a>

libc_ifunc (memmove,
            ^^^^^^^
Other uses of libc_ifunc are for example:
libc_ifunc (__strcasestr,

Attached broken fix attempt fails to build:
../sysdeps/x86_64/multiarch/memmove.c: In function '__memmove_ifunc':
../sysdeps/x86_64/multiarch/memmove.c:42:1: error: '__memmove' undeclared (first use in this function)