Avoid an implicit int in the clock_gettime test, to keep the same test
outcome with future compilers that do not support implicit ints.

Fixed upstream as part of:

r6246 | gmerlin | 2021-09-01 11:46:30 +0200 (Wed, 01 Sep 2021) | 2 lines

Applied cross-building.patch by Helmut Grohne

diff --git a/configure.ac b/configure.ac
index 90b0be6c89df4b3b..1df85ad6c222ce8d 100644
--- a/configure.ac
+++ b/configure.ac
@@ -162,7 +162,7 @@ AC_MSG_CHECKING(for CLOCK_MONOTONIC)
 AC_TRY_RUN([
   #include <time.h>
   #include <errno.h>
-main()
+int main(void)
   {
   struct timespec tp;
   if(clock_gettime(CLOCK_MONOTONIC, &tp))