I've been told to look for the "sighandler_t typedef" header, the correct file (signal.h) exists where it should be, but I don't get grep results, which is probably due to my dumbness. Any suggests for grep commands or which header?

If you know the full path for the signal.h file (mine is /usr/include/sys/signal.h) use grep this way :

Another slightly more complicated way would be to do :

First try the first way, to test your grep skills.
The second way is a funny way.
"set -x" makes the shell to be verbose, issuing each grep command.
the "find" generates the full path for each file named "something.essai.h" and gives it to the $i variable
The "grep" finds the "sighandler" string in the config.h file.
I use this more sophisticated way because there may be several signal.h on your system.
In mine, they are :