test: add makefile for test/loop

To reduce code duplication, we add a Makefile for building the
`loop` executable.

Signed-off-by: Radostin Stoyanov <rstoyanov@fedoraproject.org>

crit/Makefile

@@ -40,8 +40,8 @@ gen-proto:
 bin/crit: cmd/cli.go
 	$(GO) build ${GOFLAGS} -o $@ $^
 
-../test/loop/loop: ../test/loop/loop.c
-	$(CC) $^ -o $@
+../test/loop/loop:
+	$(MAKE) -C ../test/loop
 
 test-imgs: ../test/loop/loop
 	$(eval PID := $(shell ../test/loop/loop))

test/crit/Makefile

@@ -1,4 +1,3 @@
-CC ?= gcc
 GO ?= go
 CRIU ?= criu
 
@@ -22,8 +21,8 @@ test-imgs: ../loop/loop
 ../../crit/bin/crit:
 	$(MAKE) -C ../../crit bin/crit GOFLAGS="${GOFLAGS}"
 
-../loop/loop: ../loop/loop.c
-	$(CC) $^ -o $@
+../loop/loop:
+	$(MAKE) -C ../loop
 
 crit-test: main.go
 	$(GO) build -v -o $@ $^

test/loop/Makefile

@@ -0,0 +1,4 @@
+CC ?= gcc
+
+loop: loop.c
+	$(CC) $^ -o $@