Fix non C99 compliant check.
https://sourceforge.net/p/coan2/bugs/95/

diff --git a/configure.ac b/configure.ac
index 23ba6f0..13e6647 100644
--- configure.ac
+++ configure.ac
@@ -4,7 +4,7 @@ AC_PREREQ(2.59)
 AM_INIT_AUTOMAKE(1.13 no-define)
 AC_CHECK_HEADERS(strings.h)
 AC_MSG_CHECKING(for big-endian host)
-AC_TRY_RUN([main () {
+AC_TRY_RUN([int main () {
   /* Are we little or big endian?  From Harbison&Steele.  */
   union
   {
@@ -12,7 +12,7 @@ AC_TRY_RUN([main () {
     char c[sizeof (long)];
   } u;
   u.l = 1;
-  exit (u.c[sizeof (long) - 1] == 1);
+  return u.c[sizeof (long) - 1] == 1;
 }], BIG_ENDIAN=no, BIG_ENDIAN=yes)
 AC_MSG_RESULT([$BIG_ENDIAN])
 AM_CONDITIONAL([IS_BIG_ENDIAN],[test "$BIG_ENDIAN" = "yes"])