[OpenCL] Make is_valid_event, create_user_event overloadable.

Summary: Make is_valid_event and create_user_event overloadable like other built-ins.

Patch by Evgeniy Tyurin.

Reviewers: bader, yaxunl

Subscribers: Anastasia, cfe-commits

Differential Revision: https://reviews.llvm.org/D23914

llvm-svn: 280097
diff --git a/clang/lib/Headers/opencl-c.h b/clang/lib/Headers/opencl-c.h
index ddd2cde..9b5e2c3 100644
--- a/clang/lib/Headers/opencl-c.h
+++ b/clang/lib/Headers/opencl-c.h
@@ -16729,11 +16729,11 @@
 
 void __ovld release_event(clk_event_t);
 
-clk_event_t create_user_event(void);
+clk_event_t __ovld create_user_event(void);
 
 void __ovld set_user_event_status(clk_event_t e, int state);
 
-bool is_valid_event (clk_event_t event);
+bool __ovld is_valid_event (clk_event_t event);
 
 void __ovld capture_event_profiling_info(clk_event_t, clk_profiling_info, __global void* value);