I didn't change any compiler flags. Someone says here:

https://emacs.stackexchange.com/a/4241

that it worked when they started emacsclient from emacs/lib-src
but not when they started it from its location through
make install. So I tried starting emacs from emacs/src. I thought
debugging symbols were now on because the gdb output
looked colorful, but the log doesn't so I'm not sure.