bitrot in buildsym.c:start_subfile

[Doug Evans]

Andrew Cagney writes:
 > > In buildsym.c there's this:
 > > 
 > > /* Start recording information about source code that came from an
 > >    included (or otherwise merged-in) source file with a different
 > >    name.  NAME is the name of the file (cannot be NULL), DIRNAME is
 > >    the directory in which it resides (or NULL if not known).  */
 >
 > Guess the comment is wrong.  Any hints from the 
 > callers?

If name is NULL when subfiles is not-NULL, start_subfile will segv
in FILENAME_CMP [maybe subfiles will always be NULL when name is NULL].

What does it mean for name to be NULL?