Avoid implicit function declarations in the configure scripts.  This

avoids failures with future compilers which enforce C99 restrictions

more rigiorously.

The acsite.m4 fixes are package-specific and could be upstreamed

(if there was an upstream).

diff --git a/aclocal.m4 b/aclocal.m4

index 7b489721a47fee9f..9a726bd85f7e2d3e 100644

--- a/aclocal.m4

+++ b/aclocal.m4

@@ -4371,6 +4371,8 @@ AC_MSG_CHECKING(for working snprintf)

 AC_CACHE_VAL(ac_cv_have_working_snprintf,

 [AC_TRY_RUN(

 [#include <stdio.h>

+#include <stdlib.h>

+#include <string.h>

 int main(void)

 {

@@ -4391,6 +4393,8 @@ AC_CACHE_VAL(ac_cv_have_working_vsnprintf,

 [AC_TRY_RUN(

 [#include <stdio.h>

 #include <stdarg.h>

+#include <stdlib.h>

+#include <string.h>

 int my_vsnprintf (char *buf, const char *tmpl, ...)

 {

diff --git a/acsite.m4 b/acsite.m4

index 261ddae1935b7596..b16ac973f43944db 100644

--- a/acsite.m4

+++ b/acsite.m4

@@ -6,6 +6,8 @@ AC_MSG_CHECKING(for working snprintf)

 AC_CACHE_VAL(ac_cv_have_working_snprintf,

 [AC_TRY_RUN(

 [#include <stdio.h>

+#include <stdlib.h>

+#include <string.h>

 int main(void)

 {

@@ -26,6 +28,8 @@ AC_CACHE_VAL(ac_cv_have_working_vsnprintf,

 [AC_TRY_RUN(

 [#include <stdio.h>

 #include <stdarg.h>

+#include <stdlib.h>

+#include <string.h>

 int my_vsnprintf (char *buf, const char *tmpl, ...)

 {

diff --git a/configure b/configure

index 3a94d34938c5013b..02a683bd6f3756be 100755

--- a/configure

+++ b/configure

@@ -3942,8 +3942,8 @@ main ()

   for (i = 0; i < 256; i++)

     if (XOR (islower (i), ISLOWER (i))

         || toupper (i) != TOUPPER (i))

-      exit(2);

-  exit (0);

+      return 2;

+  return 0;

 }

 _ACEOF

 rm -f conftest$ac_exeext

@@ -6881,10 +6881,6 @@ else

 #  endif

 #endif

-#ifdef __cplusplus

-extern "C" void exit (int);

-#endif

-

 void fnord() { int i=42;}

 int main ()

 {

@@ -6898,7 +6894,7 @@ int main ()

       /* dlclose (self); */

     }

-    exit (status);

+    return status;

 }

 EOF

   if { (eval echo "$as_me:$LINENO: \"$ac_link\"") >&5

@@ -6979,10 +6975,6 @@ else

 #  endif

 #endif

-#ifdef __cplusplus

-extern "C" void exit (int);

-#endif

-

 void fnord() { int i=42;}

 int main ()

 {

@@ -6996,7 +6988,7 @@ int main ()

       /* dlclose (self); */

     }

-    exit (status);

+    return status;

 }

 EOF

   if { (eval echo "$as_me:$LINENO: \"$ac_link\"") >&5

@@ -7962,8 +7954,8 @@ main ()

   for (i = 0; i < 256; i++)

     if (XOR (islower (i), ISLOWER (i))

         || toupper (i) != TOUPPER (i))

-      exit(2);

-  exit (0);

+      return 2;

+  return 0;

 }

 _ACEOF

 rm -f conftest$ac_exeext

@@ -8605,6 +8597,8 @@ cat confdefs.h >>conftest.$ac_ext

 cat >>conftest.$ac_ext <<_ACEOF

 /* end confdefs.h.  */

 #include <stdio.h>

+#include <stdlib.h>

+#include <string.h>

 int main(void)

 {

@@ -8663,6 +8657,8 @@ cat >>conftest.$ac_ext <<_ACEOF

 /* end confdefs.h.  */

 #include <stdio.h>

 #include <stdarg.h>

+#include <stdlib.h>

+#include <string.h>

 int my_vsnprintf (char *buf, const char *tmpl, ...)

 {