package/multicat: fix HAVE_CLOCK_NANOSLEEP with uClibc

package/multicat: fix HAVE_CLOCK_NANOSLEEP with uClibc

multicat uses clock_nanosleep() conditionally if HAVE_CLOCK_NANOSLEEP is
defined. Unfortunatly, multicat does not use autoconf to check if
clock_nanosleep() is really available, but defines it if __APPLE__ is not
defined.

With uClibc clock_nanosleep() is not available if the C library is configured
without NPTL support (sets __UCLIBC_HAS_THREADS_NATIVE__) or
__UCLIBC_HAS_ADVANCED_REALTIME__ is not set.

Fixes:
http://autobuild.buildroot.net/results/84f/84f8302ee94e6e6849f6b26cb697c2f9986bafe5/
http://autobuild.buildroot.net/results/9e0/9e07a98e87755c992254295c46edb0dace967a21/
http://autobuild.buildroot.net/results/4b0/4b07d276d7c09f2fc2d63c8c37c92519cfe36dbc/
http://autobuild.buildroot.net/results/84f/84f8302ee94e6e6849f6b26cb697c2f9986bafe5/
and many more.

Upstream status: Pending
https://mailman.videolan.org/pipermail/multicat-devel/2016-March/000129.html

Signed-off-by: Jörg Krause <joerg.krause@embedded.rocks>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>