MAINTAINERS: Add myself as the maintainer for the nolibc header file(s)

I don't expect too many updates there so I should not become a
bottleneck, and if I become one, it will mean that someone will be
more active than me and will be in a better position than me to take
over maintainership.  :-)

Signed-off-by: Willy Tarreau <w@1wt.eu>
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>