package/elfutils: does not build with musl

package/elfutils: does not build with musl

elfutils uses so many GNUisms in so many places that patching them out
is a tedious task which would make us diverge so much from upstream that
it would become a nightmare to bump elfutils in the future.

Furthermore, elfutils needs argp, which is missing in musl, so it would
need argp-standalone too (as when using a uClibc toolchain).

Make elfutils depend on either glibc or uClibc. argp-standalone is
already required when using a uClibc toolchain, but since we do not
support musl, no need to add that to the condition.

Fixes (configure failures due to missing argp):
    http://autobuild.buildroot.org/results/743/7432ccd0d060a70bc35f0ac21ec92ae0071592ae/
    http://autobuild.buildroot.org/results/cc9/cc90bd9312f30f91daa50af4253629f58b82c486/
    http://autobuild.buildroot.org/results/d5e/d5e583c695afbc2e686e3002765ce9e1937aa0d5/
    [...]

Fixes (build failures due to GNUisms):
    http://autobuild.buildroot.org/results/ee7/ee7eaf80247dd96548d66be9884b179e20204a98/
    http://autobuild.buildroot.org/results/3f2/3f242853e600bb6bec6ce2f0598d304751ceb81a/
    http://autobuild.buildroot.org/results/7f0/7f0c7c9cb746104f93907544247bc1008d6ad0dc/
    [...]

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>