Get rid of support of ancient signal handler return type int

Such environments are missing void type, older K&R C, and
such supports already had been removed in various places.
Furthermore, current hardcoded 'SIGNALRETURNSINT' is wrong.

cde/programs/dtlogin/Makefile.am

@@ -39,7 +39,7 @@ libresource_a_CFLAGS = $(AM_CFLAGS) \
 		 -DDEF_SESSION=\"$(CDE_INSTALLATION_TOP)/bin/Xsession\" \
 		 -DDEF_SYSTEM_SHELL=\"/bin/sh\" \
                  -DDEF_CHOOSER=\"$(CDE_INSTALLATION_TOP)/bin/dtchooser\" \
-                 -DDEF_XDM_CONFIG=\"Xconfig\" -DSIGNALRETURNSINT \
+                 -DDEF_XDM_CONFIG=\"Xconfig\" \
 		 -DDEF_SERVER_LINE=\"":0 Local local $(DEF_SERVER) :0"\" \
                  -DXRDB_PROGRAM=\"$(XRDB)\" \
                  -DDEF_USER_PATH=\"$(DEF_USER_PATH)\" \

cde/programs/dtlogin/dm.h

@@ -161,11 +161,7 @@
 /* Utmp rec prefix */
 #define UTMPREC_PREFIX  "dt"
 
-#ifdef SIGNALRETURNSINT
-#define SIGVAL int
-#else
 #define SIGVAL void
-#endif
 
 
 #ifndef UID_NO_CHANGE

cde/programs/dtlogin/vg.h

@@ -70,11 +70,7 @@ extern int errno;
 # include <DtXinerama.h>
 #endif
 
-#ifdef SIGNALRETURNSINT
-#define SIGVAL int
-#else
 #define SIGVAL void
-#endif
 
 
 /****************************************************************************