configure: fix `HAVE_TIME_T_UNSIGNED` check

The syntax was incorrect (need a proper main body), and the test
condition was wrong (resulting in a signed `time_t` detected as
unsigned).

Closes #11825

diff --git a/configure.ac b/configure.ac
index 5c57b41d0b326fe92176293757170def557b84cf..15fbda12adc85ce15ad285331d1947eb15e3df9d 100644 (file)
--- a/configure.ac
+++ b/configure.ac
@@ -3569,8 +3569,10 @@ CURL_RUN_IFELSE(
   [
   #include <time.h>
   #include <limits.h>
-  time_t t = -1;
-  return (t > 0);
+  int main(void) {
+    time_t t = -1;
+    return (t < 0);
+  }
   ],[
   AC_MSG_RESULT([yes])
   AC_DEFINE(HAVE_TIME_T_UNSIGNED, 1, [Define this if time_t is unsigned])