Move platform specific to sys/

Move unix/ and win/ to sys/, so that we can use android/ for android
headers without confusion.

app/meson.build

@@ -12,9 +12,9 @@ src = [
 ]
 
 if host_machine.system() == 'windows'
-    src += [ 'src/win/command.c' ]
+    src += [ 'src/sys/win/command.c' ]
 else
-    src += [ 'src/unix/command.c' ]
+    src += [ 'src/sys/unix/command.c' ]
 endif
 
 dependencies = [

app/src/sys/unix/command.c

@@ -1,4 +1,4 @@
-#include "../command.h"
+#include "../../command.h"
 
 #include <signal.h>
 #include <sys/types.h>

app/src/sys/win/command.c

@@ -1,4 +1,4 @@
-#include "../command.h"
+#include "../../command.h"
 
 #include <stdio.h>
 #include "../strutil.h"