iodine: fix build issue with musl

iodine: fix build issue with musl

Fxies:
http://autobuild.buildroot.net/results/1ab/1ab4f284c9cfc2a6a42aebc6da12a766b09acc4c/
http://autobuild.buildroot.net/results/a39/a39603a143821eb4e07af42ee4ee44fdde02f9e0/
http://autobuild.buildroot.net/results/384/3847e8ef28e1527764eee18224f361115aa7063b/
http://autobuild.buildroot.net/results/899/899f8844291d384cde96475e7a9ee98b69f8c803/

Iodine contains a local implementation of daemon(3) for older systems,
unless __GLIBC__ is defined.  Musl does provide it, but unlike uClibc it
doesn't define __GLIBC__.  Work around it by pretending to be glibc as we
otherwise end up with symbol conflicts.

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>