Avoid an implicit int in the definition of the main function.
Avoids build problems with future C compilers which will not
support them by default.

Submitted upstream: <https://bz.apache.org/bugzilla/show_bug.cgi?id=66426>

diff --git a/configure.in b/configure.in
index d858951af97f3a1b..6346d8026e7a251d 100644
--- a/configure.in
+++ b/configure.in
@@ -2210,7 +2210,7 @@ AC_TRY_RUN([
 #include <sys/time.h>
 #include <sys/resource.h>
 #include <stdlib.h>
-main()
+int main(void)
 {
     struct rlimit limit;
     limit.rlim_cur = 0;