mklibs-native: fix the build on Ubuntu 9.04 by defining STT_GNU_IFUNC
mklibs-native needs elf.h (that is supplied by libc6-dev).
since STAGING_INCDIR_NATIVE doesn't contain elf.h (we don't have eglibc-native),
so the host's /usr/include/elf.h is used.
Unluckily, the libc6-dev in Ubuntu 9.04 is so old that the elf.h doesn't
define STT_GNU_IFUNC, so we have to define it ourselves.
