Remove "C" linkages (#781)

* Remove extern C linkages

* Update crc32 to cpp and remove extern C linkage

test_common/harness/conversions.h

@@ -25,10 +25,6 @@
 #include <string.h>
 #include <sys/types.h>
 
-#if defined(__cplusplus)
-extern "C" {
-#endif
-
 /* Note: the next three all have to match in size and order!! */
 
 enum ExplicitTypes
@@ -122,10 +118,6 @@ static inline int IsHalfSubnormal( cl_half x )
     return ( ( x & 0x7fffU ) - 1U ) < 0x03ffU; 
 }
 
-#if defined(__cplusplus)
-}
-#endif
-
 #endif // _conversions_h