Improve libfuzz integration (#2916)

- Allow command line tools to build together with libfuzzer driver.
  Compile everything with `-fsanitize=fuzzer-no-link` to prevent
  linking in libfuzzers's `main` symbol in all executables (causing
  duplicate symbol errors in command line tools), and add
  `-fsanitize=fuzzer` to the libfuzzer driver only.

- Make ASan optional when building with libfuzzer to allow the user
  to choose freely from available sanitizers (e.g., UBSan, MSan,
  HWASan).

- Stabilize libfuzzer by resetting PRNG seed at every invocation.

JerryScript-DCO-1.0-Signed-off-by: Akos Kiss akiss@inf.u-szeged.hu

jerry-main/CMakeLists.txt

@@ -57,7 +57,7 @@ endmacro()
 # Jerry with libfuzzer support
 if(JERRY_LIBFUZZER)
   jerry_create_executable("jerry-libfuzzer" "libfuzzer.c")
-  target_link_libraries("jerry-libfuzzer" jerry-port-default)
+  target_link_libraries("jerry-libfuzzer" jerry-port-default -fsanitize=fuzzer)
 endif()
 
 # Jerry standalones

jerry-main/libfuzzer.c

@@ -13,11 +13,14 @@
  * limitations under the License.
  */
 
+#include <stdlib.h>
+
 #include "jerryscript.h"
 
 
 int LLVMFuzzerTestOneInput (const uint8_t *data, size_t size)
 {
+  srand (0);
   jerry_init (JERRY_INIT_EMPTY);
 
   if (jerry_is_valid_utf8_string ((jerry_char_t *) data, (jerry_size_t) size))