[v1.07] Fix bug introduced by #251 (reported in #375)

PR #251 added:

```
if defined (__FreeBSD__) || defined (__APPLE__)
...
get_sys_info_by_name
```

that function is available in src/common/sysctl.c.
In the Makefile it builds with sysctl.c but only under FreeBSD:

```
ifeq ($(os), FreeBSD)
```

So it fails under macOS as reported by #375

Makefile

@@ -30,7 +30,7 @@ ifneq ($(OS),Windows_NT)
 			HEADERS += $(SRC_DIR)freq/freq.h
 			CFLAGS += -pthread
 		endif
-		ifeq ($(os), FreeBSD)
+		ifeq ($(os), $(filter $(os), FreeBSD Darwin))
 			SOURCE += $(SRC_COMMON)sysctl.c
 			HEADERS += $(SRC_COMMON)sysctl.h
 		endif