Add build.sh with RUSTFLAGS

Author: ulan

rust/image-classification/dfx.json

@@ -5,12 +5,7 @@
       "package": "backend",
       "type": "custom",
       "wasm": "target/wasm32-wasi/release/backend-ic.wasm",
-      "build": [
-         "cargo build --release --target=wasm32-wasi",
-         "wasi2ic ./target/wasm32-wasi/release/backend.wasm ./target/wasm32-wasi/release/backend-ic.wasm",
-         "wasm-opt -Os -o ./target/wasm32-wasi/release/backend-ic.wasm ./target/wasm32-wasi/release/backend-ic.wasm"
-       ]
- 
+      "build": [ "bash build.sh" ]
     },
     "frontend": {
       "dependencies": [