Everything points to a problem with the new version of Xorg-7.7-3d.tcz.
If I change nothing except replace new version of said extension with old version then reboot, then glxinfo works fine:
$ glxinfo
name of display: :0.0
display: :0 screen: 0
direct rendering: Yes
server glx vendor string: SGI
server glx version string: 1.4
server glx extensions:
GLX_ARB_create_context, GLX_ARB_create_context_no_error,
GLX_ARB_create_context_profile, GLX_ARB_fbconfig_float,
GLX_ARB_framebuffer_sRGB, GLX_ARB_multisample,
...