PR42045: Fix diagnosing enqueue_kernel call with too few args

[svenvh]

Summary

The err_typecheck_call_too_few_args diagnostic takes arguments, but
none were provided causing clang to crash when attempting to diagnose
an enqueue_kernel call with too few arguments.

[Anastasia]

LGTM! Thanks!

cfe/trunk/lib/Sema/SemaChecking.cpp

 ///                    clk_event_t *event_wait_list,
 ///                    clk_event_t *event_ret,
 ///                    void (^block)(local void*, ...),
 ///                    uint size0, ...)
 static bool SemaOpenCLBuiltinEnqueueKernel(Sema &S, CallExpr *TheCall) {
   unsigned NumArgs = TheCall->getNumArgs();
 
   if (NumArgs < 4) {
-    S.Diag(TheCall->getBeginLoc(), diag::err_typecheck_call_too_few_args);
+    S.Diag(TheCall->getBeginLoc(),
+           diag::err_typecheck_call_too_few_args_at_least)
+        << 0 << 4 << NumArgs;
     return true;
   }
 
   Expr *Arg0 = TheCall->getArg(0);
   Expr *Arg1 = TheCall->getArg(1);
   Expr *Arg2 = TheCall->getArg(2);
   Expr *Arg3 = TheCall->getArg(3);
 

cfe/trunk/test/SemaOpenCL/cl20-device-side-enqueue.cl

enqueue_kernel(default_queue, flags, ndrange, 1, &event_wait_list, &evt, // expected-error{{mismatch in number of block parameters and local size arguments passed}}
                    return 0;
                  },
                  1024, 1024, 1024);
 
   // More random misc cases that can't be deduced
   enqueue_kernel(default_queue, flags, ndrange, 1, &event_wait_list, &evt); // expected-error{{illegal call to enqueue_kernel, incorrect argument types}}
 
   enqueue_kernel(default_queue, flags, ndrange, 1, 1); // expected-error{{illegal call to enqueue_kernel, incorrect argument types}}
+
+  enqueue_kernel(default_queue, ndrange, ^{}); // expected-error{{too few arguments to function call, expected at least 4, have 3}}
 }
 
 // Diagnostic tests for get_kernel_work_group_size and allowed block parameter types in dynamic parallelism.
 kernel void work_group_size_tests() {
   void (^const block_A)(void) = ^{
     return;
   };
   void (^const block_B)(int) = ^(int a) {