Avoid calling exit without declaring the function.

Add missing <string.h> include for memcpy.

Use AC_TYPE_SIGNAL to fix REARM_SIG check.  Add missing includes.

Fix various implicit int return types of main.

Submitted upstream here: <https://sourceforge.net/p/expect/patches/24/#6759>

diff --git a/configure.in b/configure.in
index 51558fa14d2bcf7e..055c88fbd8797eaa 100755
--- a/configure.in
+++ b/configure.in
@@ -452,7 +452,11 @@ AC_CHECK_FUNC(siglongjmp, AC_DEFINE(HAVE_SIGLONGJMP))
 # because Unixware 2.0 handles it specially and refuses to compile
 # autoconf's automatic test that is a call with no arguments
 AC_MSG_CHECKING([for memcpy])
-AC_TRY_LINK(,[
+AC_TRY_LINK([
+#ifdef HAVE_STRING_H
+#include <string.h>
+#endif
+],[
 char *s1, *s2;
 memcpy(s1,s2,0);
 ],
@@ -469,6 +473,7 @@ memcpy(s1,s2,0);
 AC_MSG_CHECKING([if WNOHANG requires _POSIX_SOURCE])
 AC_TRY_RUN([
 #include <sys/wait.h>
+int
 main() {
 #ifndef WNOHANG
 	return 0;
@@ -489,6 +494,7 @@ rm -rf wnohang
 AC_TRY_RUN([
 #include <stdio.h>
 #include <sys/wait.h>
+int
 main() {
 #ifdef WNOHANG
 	FILE *fp = fopen("wnohang","w");
@@ -527,16 +533,21 @@ else
   AC_DEFINE(SELECT_MASK_TYPE, fd_set)
 fi
 
-dnl # Check for the data type of the function used in signal(). This
-dnl # must be before the test for rearming.
-dnl # echo checking return type of signal handlers
-dnl AC_HEADER_EGREP([(void|sighandler_t).*signal], signal.h, retsigtype=void,AC_DEFINE(RETSIGTYPE, int) retsigtype=int)
+AC_TYPE_SIGNAL
 
 # FIXME: check if alarm exists
 AC_MSG_CHECKING([if signals need to be re-armed])
 AC_TRY_RUN([
 #include <signal.h>
-#define RETSIGTYPE $retsigtype
+#ifdef HAVE_STDLIB_H
+# include <stdlib.h>
+#endif
+#ifdef HAVE_UNISTD_H
+# include <unistd.h>
+#endif
+#ifndef NO_SYS_WAIT_H
+# include <sys/wait.h>
+#endif
 
 int signal_rearms = 0;
 
@@ -553,6 +564,7 @@ int n;
 signal_rearms++;
 }
 
+int
 main()
 {
 	signal(SIGINT,parent_sigint_handler);
@@ -714,10 +726,11 @@ fi
 AC_MSG_CHECKING([for struct sgttyb])
 AC_TRY_RUN([
 #include <sgtty.h>
+int
 main()
 {
   struct sgttyb tmp;
-  exit(0);
+  return 0;
 }],
         AC_MSG_RESULT(yes)
         AC_DEFINE(HAVE_SGTTYB)
@@ -738,10 +751,11 @@ if test $mach -eq 0 ; then
   # pty_termios.c is set up to handle pty_termio.
   AC_MSG_CHECKING([for struct termio])
   AC_TRY_RUN([#include <termio.h>
+  int
   main()
   {
     struct termio tmp;
-    exit(0);
+    return 0;
   }],
         AC_DEFINE(HAVE_TERMIO)
         PTY_TYPE=termios
@@ -760,10 +774,11 @@ if test $mach -eq 0 ; then
 #  include <inttypes.h>
 #  endif
 #  include <termios.h>
+  int
   main()
   {
     struct termios tmp;
-    exit(0);
+    return 0;
   }],
         AC_DEFINE(HAVE_TERMIOS)
         PTY_TYPE=termios
@@ -782,6 +797,7 @@ AC_TRY_RUN([
 #include <inttypes.h>
 #endif
 #include <termios.h>
+int
 main() {
 #if defined(TCGETS) || defined(TCGETA)
 	return 0;
@@ -804,6 +820,7 @@ AC_TRY_RUN([
 #include <inttypes.h>
 #endif
 #include <termios.h>
+int
 main() {
 #ifdef TIOCGWINSZ
 	return 0;
@@ -823,6 +840,7 @@ main() {
 AC_MSG_CHECKING([for Cray-style ptys])
 SETUID=":"
 AC_TRY_RUN([
+int
 main(){
 #ifdef CRAY
 	return 0;
@@ -878,12 +896,13 @@ AC_MSG_CHECKING([for SV-style timezone])
 AC_TRY_RUN([
 extern char *tzname[2];
 extern int daylight;
+int
 main()
 {
   int *x = &daylight;
   char **y = tzname;
 
-  exit(0);
+  return 0;
 }],
 	AC_DEFINE(HAVE_SV_TIMEZONE)
 	AC_MSG_RESULT(yes),
diff --git a/tclconfig/tcl.m4 b/tclconfig/tcl.m4
index 0689cab3da994068..ebe839e5553ba520 100644
--- a/tclconfig/tcl.m4
+++ b/tclconfig/tcl.m4
@@ -2400,7 +2400,7 @@ AC_DEFUN([TEA_TIME_HANDLER], [
 	AC_TRY_COMPILE([#include <time.h>],
 	    [extern long timezone;
 	    timezone += 1;
-	    exit (0);],
+	    return 0;],
 	    tcl_cv_timezone_long=yes, tcl_cv_timezone_long=no)])
     if test $tcl_cv_timezone_long = yes ; then
 	AC_DEFINE(HAVE_TIMEZONE_VAR, 1, [Should we use the global timezone variable?])
@@ -2412,7 +2412,7 @@ AC_DEFUN([TEA_TIME_HANDLER], [
 	    AC_TRY_COMPILE([#include <time.h>],
 		[extern time_t timezone;
 		timezone += 1;
-		exit (0);],
+		return 0;],
 		tcl_cv_timezone_time=yes, tcl_cv_timezone_time=no)])
 	if test $tcl_cv_timezone_time = yes ; then
 	    AC_DEFINE(HAVE_TIMEZONE_VAR, 1, [Should we use the global timezone variable?])
@@ -2452,17 +2452,17 @@ AC_DEFUN([TEA_BUGGY_STRTOD], [
 		    double value;
 		    value = strtod(infString, &term);
 		    if ((term != infString) && (term[-1] == 0)) {
-			exit(1);
+			return 1;
 		    }
 		    value = strtod(nanString, &term);
 		    if ((term != nanString) && (term[-1] == 0)) {
-			exit(1);
+			return 1;
 		    }
 		    value = strtod(spaceString, &term);
 		    if (term == (spaceString+1)) {
-			exit(1);
+			return 1;
 		    }
-		    exit(0);
+		    return 0;
 		}], tcl_cv_strtod_buggy=ok, tcl_cv_strtod_buggy=buggy,
 		    tcl_cv_strtod_buggy=buggy)])
 	if test "$tcl_cv_strtod_buggy" = buggy; then