[HIPIFY][win] Set -std=c++14 if MSVC

+ Due to latest Windows SDK implementation based on c++14 features, '-std+c++14' is a must;
+ Doesn't affect older versions of MSVC 2017, 2015 (the latest supported is MSVC 2015);
+ On linux still '-std=c++11' is a must;
+ Exclude '-std=' from lit config.


[ROCm/hip commit: 2d3f62c3e1]

projects/hip/tests/hipify-clang/lit.cfg

@@ -65,7 +65,7 @@ clang_args = "-x cuda -v --cuda-gpu-arch=sm_30 --cuda-path='%s'"
 if sys.platform in ['win32']:
     run_test_ext = ".bat"
     hipify_path += "/" + config.build_type
-    clang_args += " -isystem'%s'/common/inc -std=c++14"
+    clang_args += " -isystem'%s'/common/inc"
 else:
     run_test_ext = ".sh"
     clang_args += " -isystem'%s'/samples/common/inc"