Remove "C" linkages (#781)

* Remove extern C linkages

* Update crc32 to cpp and remove extern C linkage

test_common/harness/crc32.h

@@ -21,14 +21,6 @@ executed between Khronos and the recipient.
 #include <stdint.h> 
 #include <stddef.h>
 
-#ifdef __cplusplus
-extern "C" {
-#endif
-
 uint32_t crc32(const void *buf, size_t size);
 
-#ifdef __cplusplus
-}
-#endif
-
 #endif