message: meson: default to -O3 optimizations
  This will be overriden if meson is run with --buildtype debug, for example.
diff: project('freebayes', ['cpp', 'c'],
  version : '1.3.4',
  - default_options : ['warning_level=1', 'cpp_std=c++14'])
  + default_options : ['warning_level=1', 'cpp_std=c++14', 'optimization=3'])
  cc = meson.get_compiler('cpp')
  