Add integration test

Makefile

@@ -1,6 +1,6 @@
 .PHONY: all test clean
 
-all: c2 test
+all: c2 test integration-test
 
 c2: v0/bin/c2
 	cp $< $@

v0/integration_tests/simple/expected.c

@@ -1 +1,4 @@
-Hello, world
+#include <stdint.h>
+
+// u32 simple:x
+static uint32_t v_6simple_1x = 123;