gengtype and automatically generated files

[Bill Schmidt via Gcc]

Hi!  I'm attempting to do something that may not have been done before, 
so I'm looking for advice, or a pointer to where, in fact, it has been 
done before. :)

I'm automatically generating a back-end header file that declares some 
structures that include trees, and a bunch of global variables that are 
also trees.  I've marked everything up appropriately, but I also need to 
teach the garbage collector that this file exists.

Most back-end files are automatically scanned by gengtype.  Per the 
documentation, anything that isn't handled automatically needs to be 
added to target_gtfiles in config.gcc.  However, I can't come up with a 
syntax for describing a file in the gcc/ build subdirectory.  Some 
places in config.gcc allow "./filename" as shorthand for "filename" 
being in the current build directory, but that doesn't seem to work for 
adding something to gtyp-input.list.

Any recommendations on what I should do next?  At the moment it looks 
like I might have to hack on gengtype to invent a way to scan a file in 
the build directory, but I have a mild amount of hope that someone has 
solved this before.  Thanks for any help!

Bill