Hi, everyone,
There is an update-everything command you might want to run to make sure all .dep and md5 files are correct.
If any errors crop up, especially missing md5 files, that might explain some of the problems you had.
I can confirm that update-everything fixed the problem with Xorg not starting in the machines I mentioned before (Intel i915 and NVIDIA nForce 610i).
There are unmet dependencies on libEGL and libGL in xorg-server that would be used by Xorg-7.7-3d.
Juanito is right. On both machines I was loading Xorg-7.7-3d. That is why the dependency on llvm19-lib.tcz in my /var/log/Xorg.0.
Now in the machine with intel chipset, Xorg can starts with xf86-video-intel.tcz and Xorg-7.7.tcz; in the nvidia chipset can starts with nouveau-6.12.11-tinycore.tcz and Xorg-7.7.tcz (or even Xorg-7.7-3d.tcz).
On the machine (intel) in which I now write on, xorg-server.tcz.dep shows
libXfont2.tcz
libepoxy.tcz
expat2.tcz
openssl.tcz
pixman.tcz
libxcvt.tcz
libpciaccess.tcz
libxshmfence.tcz
libdrm.tcz
xkbcomp.tcz
(By the way, gedit was working before the update. Now it complains about "error while loading shared libraries: libglapi.so.0: cannot open shared object file: No such file or directory". But emacs works great

)
Thank you all for your help.