Add missing alias half / half2 aliases

[ROCm/hip commit: 98395ad38c]

projects/hip/include/hip/hcc_detail/hip_fp16_gcc.h

@@ -248,5 +248,10 @@ struct __half2_raw {
         {
             return __internal_half2float(static_cast<__half2_raw>(x).y);
         }
-    }
-#endif // defined(__cplusplus)
+    } // Anonymous namespace.
+
+    #if !defined(HIP_NO_HALF)
+        using half = __half;
+        using half2 = __half2;
+    #endif
+#endif // defined(__cplusplus)