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>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@45752 3c298f89-4303-0410-b956-a3cf2f4a3e73