code: def generate(env):
      
      add_all_to_env(env)
      add_f77_to_env(env)
  
      fcomp = env.Detect(compilers) or 'g77'
      if env['PLATFORM'] in ['cygwin', 'win32']:
          env['SHFORTRANFLAGS'] = SCons.Util.CLVar('$FORTRANFLAGS')
          env['SHF77FLAGS'] = SCons.Util.CLVar('$F77FLAGS')
      else:
          env['SHFORTRANFLAGS'] = SCons.Util.CLVar('$FORTRANFLAGS -fPIC')
          env['SHF77FLAGS'] = SCons.Util.CLVar('$F77FLAGS -fPIC')
  
      env['FORTRAN'] = fcomp
      env['SHFORTRAN'] = '$FORTRAN'
  
      env['F77'] = fcomp
      env['SHF77'] = '$F77'
  
      env['INCFORTRANPREFIX'] = "-I"
      env['INCFORTRANSUFFIX'] = ""
  
      env['INCF77PREFIX'] = "-I"
      env['INCF77SUFFIX'] = ""
docs: Add Builders and construction variables for g77 to an Environment.