fix compilation of native gems required for installing fpm

"build-essential" was being installed by setup-mingw-w64 but
not by the setup-schroot-xxx targets, fixes #2478

scripts/build.py

@@ -727,7 +727,7 @@ def check_setup_schroot(config):
 
 def build_setup_schroot(config, basedir):
     install_packages('git', 'debootstrap', 'schroot', 'rinse', 'debian-archive-keyring',
-                     'ruby', 'ruby-dev', 'libffi-dev', 'tar', 'xz-utils')
+                     'build-essential', 'ruby', 'ruby-dev', 'libffi-dev', 'tar', 'xz-utils')
     if not get_output('which', 'fpm'):
         shell('gem install -V fpm -N')