m4: Update manywarnings from gnulib
m4: Update manywarnings from gnulib

Fixes these noisy errors on Fedora 21:

gcc: warning: switch '-Wmudflap' is no longer supported

SPICE/spice,elmarco/spice,ya-mouse/spice,fgouget/spice,fgouget/spice,fgouget/spice,ya-mouse/spice,freedesktop-unofficial-mirror/spice__spice,fgouget/spice,Fantu/spice,elmarco/spice,elmarco/spice,elmarco/spice,freedesktop-unofficial-mirror/spice__spice,SPICE/spice,Fantu/spice,SPICE/spice,ya-mouse/spice,freedesktop-unofficial-mirror/spice__spice,freedesktop-unofficial-mirror/spice__spice,Fantu/spice,elmarco/spice,Fantu/spice,freedesktop-unofficial-mirror/spice__spice