add Makefile prerequisites

Signed-off-by: MorningTZH <morningtzh@yeah.net>

Makefile

@@ -14,11 +14,13 @@ SYSTEMD_CONF_DIR := /etc/sysconfig
 
 all: vmm quark wasm
 
-bin/vmm-sandboxer:
+vmm-sandboxer-sources := $(shell find vmm/sandbox -type f)
+bin/vmm-sandboxer: $(vmm-sandboxer-sources)
 	@cd vmm/sandbox && cargo build --release --bin ${HYPERVISOR}
 	@mkdir -p bin && cp vmm/sandbox/target/release/${HYPERVISOR} bin/vmm-sandboxer
 
-bin/vmm-task:
+vmm-task-sources := $(shell find vmm/task -type f)
+bin/vmm-task: $(vmm-task-sources)
 	@cd vmm/task && cargo build --release --target=${ARCH}-unknown-linux-musl
 	@mkdir -p bin && cp vmm/task/target/${ARCH}-unknown-linux-musl/release/vmm-task bin/vmm-task
 
@@ -34,15 +36,18 @@ bin/kuasar.initrd:
 	@bash -x vmm/scripts/image/${GUESTOS_IMAGE}/build.sh initrd
 	@mkdir -p bin && cp /tmp/kuasar.initrd bin/kuasar.initrd && rm /tmp/kuasar.initrd
 
-bin/wasm-sandboxer:
+wasm-sources := $(shell find wasm -type f)
+bin/wasm-sandboxer: $(wasm-sources)
 	@cd wasm && cargo build --release --features=${WASM_RUNTIME}
 	@mkdir -p bin && cp wasm/target/release/wasm-sandboxer bin/wasm-sandboxer
 
-bin/quark-sandboxer:
+quark-sources := $(shell find quark -type f)
+bin/quark-sandboxer: $(quark-sources)
 	@cd quark && cargo build --release
 	@mkdir -p bin && cp quark/target/release/quark-sandboxer bin/quark-sandboxer
 
-bin/runc-sandboxer:
+runc-sources := $(shell find runc -type f)
+bin/runc-sandboxer: $(runc-sources)
 	@cd runc && cargo build --release
 	@mkdir -p bin && cp runc/target/release/runc-sandboxer bin/runc-sandboxer