pgf77 can be used in place of and is compatible with g77. We do have a flag “-g77libs” which adds all necessary g77 libraries, including “-lg2c” to the link line. However if you prefer, since “-lg2c” is a library, it can simply be added to the link line.
Note that g77 adds two underscores to the end of function names while pgf77 only adds one. If you mix g77 and pgf77 compiled objects, you may need to add the flag “-Msecond_underscore” to the pgf77 compilation line to instruct pgf77 to use two underscores instead of one.