elfutils: make available on uClibc toolchains

We finally have all the pieces needed to allow the build of elfutils
on uClibc. Only the libraries can be built, the programs remain
available only for glibc/eglibc toolchains.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>