[libFuzzer] make LLVMFuzzerTestOneInput (the fuzzer target function) return int instead of void. The actual return value is not *yet* used (and expected to be 0). This change is API breaking, so the fuzzers will need to be updated.

llvm-svn: 249214
diff --git a/llvm/lib/Fuzzer/test/NullDerefTest.cpp b/llvm/lib/Fuzzer/test/NullDerefTest.cpp
index 0cff661..200c56c 100644
--- a/llvm/lib/Fuzzer/test/NullDerefTest.cpp
+++ b/llvm/lib/Fuzzer/test/NullDerefTest.cpp
@@ -7,7 +7,7 @@
 static volatile int Sink;
 static volatile int *Null = 0;
 
-extern "C" void LLVMFuzzerTestOneInput(const uint8_t *Data, size_t Size) {
+extern "C" int LLVMFuzzerTestOneInput(const uint8_t *Data, size_t Size) {
   if (Size > 0 && Data[0] == 'H') {
     Sink = 1;
     if (Size > 1 && Data[1] == 'i') {
@@ -18,5 +18,6 @@
       }
     }
   }
+  return 0;
 }