package/protobuf: autoreconf is now needed

Since its update, the *_SITE points to the git repository, so configure
script is not generated in this tarball.

Fixes:
  http://autobuild.buildroot.org/results/ccb/ccba6d8c73b5e826b86065b77b3fe5077db7b99c/
  http://autobuild.buildroot.org/results/57e/57ea34e9b48293075e10f0dd2331de2785730827/


  and many more...

[Peter: drop redundant HOST_*_AUTORECONF]
Signed-off-by: Samuel Martin <s.martin49@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>