patch 8.2.1119: configure fails with Xcode 12 beta

Problem:    Configure fails with Xcode 12 beta.
Solution:   use "return" instead of "exit()". (Nico Weber, closes #6381)
diff --git a/src/auto/configure b/src/auto/configure
index f642a0b..9c9a719 100755
--- a/src/auto/configure
+++ b/src/auto/configure
@@ -14143,8 +14143,8 @@
 main() {
   uint32_t nr1 = (uint32_t)-1;
   uint32_t nr2 = (uint32_t)0xffffffffUL;
-  if (sizeof(uint32_t) != 4 || nr1 != 0xffffffffUL || nr2 + 1 != 0) exit(1);
-  exit(0);
+  if (sizeof(uint32_t) != 4 || nr1 != 0xffffffffUL || nr2 + 1 != 0) return 1;
+  return 0;
 }
 _ACEOF
 if ac_fn_c_try_run "$LINENO"; then :