docs: def prepare_build_dir(self):
          '''Ensure that a build dir exists for the recipe. This same single
          dir will be used for building all different archs.'''
          self.build_dir = self.get_build_dir()
          self.common_dir = self.get_common_dir()
          copy_files(join(self.bootstrap_dir, 'build'), self.build_dir)
          copy_files(join(self.common_dir, 'build'), self.build_dir,
                     override=False)
          if self.ctx.symlink_java_src:
              info('Symlinking java src instead of copying')
              shprint(sh.rm, '-r', join(self.build_dir, 'src'))
              shprint(sh.mkdir, join(self.build_dir, 'src'))
              for dirn in listdir(join(self.bootstrap_dir, 'build', 'src')):
                  shprint(sh.ln, '-s', join(self.bootstrap_dir, 'build', 'src', dirn),
                          join(self.build_dir, 'src'))
          with current_directory(self.build_dir):
              with open('project.properties', 'w') as fileh:
                  fileh.write('target=android-{}'.format(self.ctx.android_api))