fix compilation error when host compiler is clang (#1147)

* fix compilation error when host compiler is clang

* use a macro specifically for hcc && hip-clang

include/hip/hcc_detail/hip_fp16.h

@@ -34,7 +34,7 @@ THE SOFTWARE.
     #include <utility>
 #endif
 
-#if defined(__clang__) && (__clang_major__ > 5)
+#if __HCC_OR_HIP_CLANG__
     typedef _Float16 _Float16_2 __attribute__((ext_vector_type(2)));
 
     struct __half_raw {