docs: def compile_extensions(macros, compat=False):
      """
      Compiler subroutine to test whether some functions are available
      on the target system. Since the rrdtool headers shipped with most
      packages do not disclose any versioning information, we cannot test
      whether a given function is available that way. Instead, use this to
      manually try to compile code and see if it works.
  
      Taken from http://stackoverflow.com/questions/28843765/setup-py-check-if-non-python-library-dependency-exists.
      """
      import distutils.sysconfig
      import distutils.ccompiler
      import tempfile
      import shutil
  
      from textwrap import dedent
  
      # common vars
      libraries = ['rrd']
      include_dirs = [package_dir, '/usr/local/include']
      library_dirs = ['/usr/local/lib']
      compiler_args = dict(
          libraries=libraries,
          include_dirs=include_dirs,
          library_dirs=library_dirs,
          define_macros=macros)
      exts = [Extension('rrdtool', sources=['rrdtoolmodule.c'], **compiler_args)]
  
      if compat:
          return exts
  
      # in non-compat mode, try to link to check if the new symbols are present in librrd
      c_code = dedent('''
          #include <rrd.h>
          #include "rrdtoolmodule.h"
  
          int main(int argc, char *argv[]) {
              rrd_fetch_cb_register(NULL);  /* exists in rrdtool >= 1.5.0 */
              return 0;
          }
      ''')
  
      tmp_dir = tempfile.mkdtemp(prefix='tmp_python_rrdtool')
      bin_file_name = os.path.join(tmp_dir, 'test_rrdtool')
      file_name = bin_file_name + '.c'
  
      with open(file_name, 'w') as fp:
          fp.write(c_code)
  
      # try to compile it
      compiler = distutils.ccompiler.new_compiler()
      assert isinstance(compiler, distutils.ccompiler.CCompiler)
      for s in include_dirs:
          compiler.add_include_dir(s)
      for s in library_dirs:
          compiler.add_library_dir(s)
      for s in libraries:
          compiler.add_library(s)
      for s in macros:
          compiler.define_macro(*s)
      distutils.sysconfig.customize_compiler(compiler)
  
      try:
          compiler.link_executable(
              compiler.compile([file_name]),
              bin_file_name,
              libraries=libraries)
      except CompileError:
          sys.exit('Error: Unable to compile the binary module. Do you have the rrdtool header and libraries installed?')
          ret = None
      except LinkError as exc:
          shutil.rmtree(tmp_dir)
          raise  # re-raise
      else:
          return exts  # seems to be available, compile in regular way
  
      shutil.rmtree(tmp_dir)
      return ret