libgtop fails to build on musl libc, due to the header
resulting in the headers that would be loaded for libc 5 being
loaded on musl libc.
musl defines headers which are also defined in linux-headers'
in.h, causing redefinition errors.
https://bugzilla.gnome.org/show_bug.cgi?id=760655
Signed-off-by: Benoît Dejean <bdejean@gmail.com>