Include CompilerRTCompile in fuzzer tests explicitly. Otherwise, when
building only libFuzzer, CMake fails due to:
CMake Error at cmake/Modules/AddCompilerRT.cmake:395 (sanitizer_test_compile): Unknown CMake command "sanitizer_test_compile". Call Stack (most recent call first): lib/fuzzer/tests/CMakeLists.txt:53 (generate_compiler_rt_tests)