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

Remove hacks to force language from CMake files.

Closes KhronosGroup/OpenCL-CTS#25

test_conformance/vec_align/CMakeLists.txt

@@ -1,11 +1,11 @@
 set(MODULE_NAME VECALIGN)
 
 set(${MODULE_NAME}_SOURCES
-    globals.c
-        main.c
-        structs.c
-        test_vec_align.c
-        type_replacer.c
+    globals.cpp
+        main.cpp
+        structs.cpp
+        test_vec_align.cpp
+        type_replacer.cpp
 )
 
 set_source_files_properties(