[libFuzzer] Do not use LLVM ostream in libFuzzer tests.

[george.karpenkov]

Summary

LibFuzzer aims to have no LLVM dependencies, yet using gtest introduces a dependency on LLVM ostream, unless explicitly requested not to.
This change removes the dependency, and makes potential subsequent build system change much easier.

[kcc]

LGTM
libFuzzer *must* not have LLVM deps, but tests can.
But in this case there is clearly no reason to use custom LLVM ostream

runtimes/libfuzzer/test/FuzzerUnittest.cpp

 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 
 // Avoid ODR violations (LibFuzzer is built without ASan and this test is built
 // with ASan) involving C++ standard library types when using libcxx.
 #define _LIBCPP_HAS_NO_ASAN
 
+// Do not attempt to use LLVM ostream from gtest.
+#define GTEST_NO_LLVM_RAW_OSTREAM 1
+
 #include "FuzzerCorpus.h"
 #include "FuzzerDictionary.h"
 #include "FuzzerInternal.h"
 #include "FuzzerMerge.h"
 #include "FuzzerMutate.h"
 #include "FuzzerRandom.h"
 #include "FuzzerTracePC.h"
 #include "gtest/gtest.h"