Merge #21080: fuzz: Configure check for main function (take 2)

fac4be3048 fuzz: Configure check for main function (take 2) (MarcoFalke)

Pull request description:

  Actually fix https://github.com/google/honggfuzz/issues/336#issuecomment-702972138

  Follow-up to #20065

  Steps to test: `honggfuzz` section in doc/fuzzing.md

ACKs for top commit:
  practicalswift:
    cr ACK fac4be30482c21ac330e09ef8756c49e37faa6fa: patch looks correct!

Tree-SHA512: 893768c80439fe5d90b883ade89dc02f5bb80e27637916cf5575b6a9ed0b1c04942ff851342f5bbabb8666e6696715427feeb98f5301ad23c7b87b09e5872f97

configure.ac

@@ -1254,8 +1254,10 @@ if test "x$enable_fuzz" = "xyes"; then
       #include <cstdint>
       #include <cstddef>
       extern "C" int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) { return 0; }
-      /* unterminated comment to remove the main function ...
-    ]],[[]])])
+      /* comment to remove the main function ...
+     ]],[[
+      */ int not_main() {
+     ]])])
 else
   BITCOIN_QT_INIT