problem with compiling maxima 5.6



     Correctable error: (SYSTEM "(cd . ;gcc -pipe -fwritable-strings
     -DVOL=volatile -I/home/michel/download/gcl-2.4.0/o -fsigned-char
     -O4 -c -I. sysinit.c -w)") returned a non-zero value 0.

Somehow either you have moved the gcl from where you built it or removed
cmpinclude.h from your directory /home/michel/download/gcl-2.4.0/o.

such thing, since the cmpinclude.h is in gcl-2.4.0/o  among other directories and that is in the gcc command line that is being passed.
Under the target all: in the main makefile, is the line.
	rm -f o/cmpinclude.h ; ln h/cmpinclude.h o
so there should be a copy there.