tests: use go test -a to work around Go caching

Go does not notice when the C code changes, so we have to
use `go test -a`.

Workaround for golang/go#24355 .

Author: rfjakob

Makefile

@@ -81,4 +81,6 @@ format: earlyoom
 	clang-format -i *.h *.c
 
 test: earlyoom
-	cd tests ; go test -v
+	# Go does not notice when the C code changes, so we have to
+	# use `go test -a`. See https://github.com/golang/go/issues/24355 .
+	cd tests && go test -a -v