fix WASM_ENABLE_WASI_EPHEMERAL_NN build

this structure is used by host logic as well.
ideally definitions for wasm and host should be separated.
until it happens, check __wasm__ to avoid the breakage.

Author: yamt

core/iwasm/libraries/wasi-nn/include/wasi_nn_types.h

@@ -77,7 +77,7 @@ typedef struct {
     // Describe the size of the tensor (e.g., 2x2x2x2 -> [2, 2, 2, 2]). To
     // represent a tensor containing a single value, use `[1]` for the tensor
     // dimensions.
-#if WASM_ENABLE_WASI_EPHEMERAL_NN != 0
+#if WASM_ENABLE_WASI_EPHEMERAL_NN != 0 && defined(__wasm__)
     tensor_dimensions dimensions;
 #else
     tensor_dimensions *dimensions;