Rename test .c sources to .cpp where necessary (#604)

Remove hacks to force language from CMake files.

Closes KhronosGroup/OpenCL-CTS#25

test_conformance/multiple_device_context/main.cpp

@@ -0,0 +1,46 @@
+//
+// Copyright (c) 2017 The Khronos Group Inc.
+// 
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//    http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+#include "harness/compat.h"
+
+#include <stdio.h>
+#include <string.h>
+#include "procs.h"
+#include "harness/testHarness.h"
+#include "harness/mt19937.h"
+
+#if !defined(_WIN32)
+#include <unistd.h>
+#endif
+
+test_definition test_list[] = {
+    ADD_TEST( context_multiple_contexts_same_device ),
+    ADD_TEST( context_two_contexts_same_device ),
+    ADD_TEST( context_three_contexts_same_device ),
+    ADD_TEST( context_four_contexts_same_device ),
+
+    ADD_TEST( two_devices ),
+    ADD_TEST( max_devices ),
+
+    ADD_TEST( hundred_queues ),
+};
+
+const int test_num = ARRAY_SIZE( test_list );
+
+int main(int argc, const char *argv[])
+{
+    return runTestHarness( argc, argv, test_num, test_list, false, true, 0 );
+}
+