Problem building from Source

I am trying to build GPS from source (currently under Solaris).

I realize there is a pre-built binary but I am (currently) interested in 
a source build.
I've got a working GtkAda-2.4.0 and Gtk (and all dependancies). Using 
GCC 3.4.1.

When I try to compile GPS I get an error after it complete the Making 
all in db and does the gnatmake -Pgps gps.adb.

The problem is when compiling external_editor_module.adb that it decides 
that gdk.ads needs to
be recompiled but it can't because gdk.ali is readonly (as it should be 
after the install)

It somewhat looks as if there is a problem where it thinks gdk.ads needs 
to be recompiled. Normal GtkAda user programs
don't run into this problem. I am (somewhat) guessing (after adding a -v 
to the project switches) that what is
happening here is that the pieces of gnat source that get distributed 
with GPS are being used and there is (somehow) a dependancy of gdk.ads on
some system files.

In any case, something odd is happening and there does not appear to be 
any magic
required in the INSTALL readme that comes with gps that indicates this 
should happen.

It seems to me like the documentation is broken or I am missing 
something really obvious.