uClibc: elf: Add STT_GNU_IFUNC from glibc

perf in upstream Linux kernel 3.17 onwards expects STT_GNU_IFUNC
replicate it from glibc

Patch cherry-picked from:
http://lists.busybox.net/pipermail/uclibc/2015-February/048825.html



Signed-off-by: Mathieu Olivari <mathieu@codeaurora.org>

SVN-Revision: 45752