Rename harness .c sources to .cpp where necessary (#513)

Remove hacks from harness CMakeLists.txt to force language.

Contributes to KhronosGroup/OpenCL-CTS#25

test_common/CMakeLists.txt

@@ -1,33 +1,29 @@
 
 set(HARNESS_COMMON_SOURCES
-    harness/threadTesting.c
+    harness/threadTesting.cpp
     harness/typeWrappers.cpp
     harness/mt19937.c
-    harness/conversions.c
+    harness/conversions.cpp
     harness/rounding_mode.c
     harness/msvc9.c
 )
 
-set_source_files_properties(${HARNESS_COMMON_SOURCES} PROPERTIES LANGUAGE CXX)
-
 add_library(harness-common STATIC ${HARNESS_COMMON_SOURCES})
 
 set(HARNESS_SOURCES
     harness/crc32.c
-    harness/errorHelpers.c
+    harness/errorHelpers.cpp
     harness/genericThread.cpp
     harness/imageHelpers.cpp
-    harness/kernelHelpers.c
+    harness/kernelHelpers.cpp
     harness/deviceInfo.cpp
     harness/os_helpers.cpp
     harness/parseParameters.cpp
-    harness/testHarness.c
-    harness/ThreadPool.c
+    harness/testHarness.cpp
+    harness/ThreadPool.cpp
     miniz/miniz.c
 )
 
-set_source_files_properties(${HARNESS_SOURCES} PROPERTIES LANGUAGE CXX)
-
 add_library(harness STATIC ${HARNESS_SOURCES})
 
 target_link_libraries(harness harness-common)