I did load the pkg-config extension, but Emacs' ./configure script wasn't finding libpng or freetype2. (I hadn't set PKG_CONFIG_PATH). I didn't realize this was the problem so I followed bmarkus and downloaded and compiled both libpng and freetype 2. Finally, I found a third missing dependency in /usr/lib/packageconfig (or /usr/local/lib/pkgconfig, I forget) and I set PKG_CONFIG_PATH to include it, and it configured.
However things broke during compiling with a mysterious error which reported as if it were an error in the source code (possible, but they're releasing the Emacs pretest packages verrrrry conservatively just now, and I did compile an earlier version sucessfully under TC 1.3.) I'd send the error (and could), but I'm on a different machine just now.
Could it be that I caused myself trouble by compiling new versions of libpng and freetype2, rather than using the versions in the TC compile environment? (The TC environment was there, but my new versions were in /usr/local/..., so I assume they were used) Or could I have caused myself trouble by mixing tcz and tce extensions for the development tools?
Thanks for your earlier help.