[Sanitizers] Check pthread_setcancel{state|type} interceptor arguments for != nullptr.

[alekseyshl]

Summary

According to man, pthread_setcancelstate's oldstate and
pthread_setcanceltype's oldtype parameters can be nullptr.
Check these parameters for != nullptr before attempting to
access their shadow memory.

compiler-rt/trunk/lib/sanitizer_common/sanitizer_common_interceptors.inc

 #define INIT_SEM
 #endif // SANITIZER_INTERCEPT_SEM
 
 #if SANITIZER_INTERCEPT_PTHREAD_SETCANCEL
 INTERCEPTOR(int, pthread_setcancelstate, int state, int *oldstate) {
   void *ctx;
   COMMON_INTERCEPTOR_ENTER(ctx, pthread_setcancelstate, state, oldstate);
   int res = REAL(pthread_setcancelstate)(state, oldstate);
-  if (res == 0)
+  if (res == 0 && oldstate != nullptr)
     COMMON_INTERCEPTOR_WRITE_RANGE(ctx, oldstate, sizeof(*oldstate));
   return res;
 }
 
 INTERCEPTOR(int, pthread_setcanceltype, int type, int *oldtype) {
   void *ctx;
   COMMON_INTERCEPTOR_ENTER(ctx, pthread_setcanceltype, type, oldtype);
   int res = REAL(pthread_setcanceltype)(type, oldtype);
-  if (res == 0)
+  if (res == 0 && oldtype != nullptr)
     COMMON_INTERCEPTOR_WRITE_RANGE(ctx, oldtype, sizeof(*oldtype));
   return res;
 }
 #define INIT_PTHREAD_SETCANCEL                                                 \
   COMMON_INTERCEPT_FUNCTION(pthread_setcancelstate);                           \
   COMMON_INTERCEPT_FUNCTION(pthread_setcanceltype);
 #else
 #define INIT_PTHREAD_SETCANCEL