glib/gmain.c uses signal() but does not include signal.h.
Trivial patch to include signal.h attached.

Makefile and compiler output:
/bin/bash ../libtool --mode=compile cc -DHAVE_CONFIG_H -I. -I. -I.. -I..
-DG_LOG_DOMAIN=\"GLib\" -DG_ENABLE_DEBUG -DG_DISABLE_DEPRECATED
-DGLIB_COMPILATION   -I/opt/gnome-2.4/include -mt  -g
-I/opt/gnome-2.4/include -c -o gmain.lo `test -f 'gmain.c' || echo './'`gmain.c
 cc -DHAVE_CONFIG_H -I. -I. -I.. -I.. -DG_LOG_DOMAIN=\"GLib\"
-DG_ENABLE_DEBUG -DG_DISABLE_DEPRECATED -DGLIB_COMPILATION
-I/opt/gnome-2.4/include -mt -g -I/opt/gnome-2.4/include -c gmain.c  -KPIC
-DPIC -o .libs/gmain.o
"gmain.c", line 3338: warning: implicit function declaration: signal
"gmain.c", line 3338: undefined symbol: SIGCHLD
"gmain.c", line 3374: warning: statement not reached
"gmain.c", line 3393: undefined symbol: SIGCHLD
cc: acomp failed for gmain.c
make[3]: *** [gmain.lo] Error 1