bison: add host-m4 as dependency

Pull in host-m4 as dependency since it requires a new-enough m4 to build
properly and some distributions don't update that often. Fixes:
http://autobuild.buildroot.net/results/ee8/ee88f2c2a80dc19699d176ff2acde62fbc8a251f/



Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>