[OpenCL] Rename lang mode flag for C++ mode

Rename lang mode flag to -cl-std=clc++/-cl-std=CLC++
or -std=clc++/-std=CLC++.

This aligns with OpenCL C conversion and removes ambiguity
with OpenCL C++. 

Differential Revision: https://reviews.llvm.org/D65102

llvm-svn: 367008
diff --git a/clang/lib/Frontend/CompilerInvocation.cpp b/clang/lib/Frontend/CompilerInvocation.cpp
index 503e1fd..6bf4fbc 100644
--- a/clang/lib/Frontend/CompilerInvocation.cpp
+++ b/clang/lib/Frontend/CompilerInvocation.cpp
@@ -2433,7 +2433,7 @@
         .Cases("cl1.1", "CL1.1", LangStandard::lang_opencl11)
         .Cases("cl1.2", "CL1.2", LangStandard::lang_opencl12)
         .Cases("cl2.0", "CL2.0", LangStandard::lang_opencl20)
-        .Case("c++", LangStandard::lang_openclcpp)
+        .Cases("clc++", "CLC++", LangStandard::lang_openclcpp)
         .Default(LangStandard::lang_unspecified);
 
     if (OpenCLLangStd == LangStandard::lang_unspecified) {