Squashed commit of the following:

binfmt/, configs/, grahics/, libc/, mm/, net/, sched/:  OS references to the errno variable should always use the set_errno(), get_errno() macros
    arch/arm/src/stm32 and stm32f7:  Architecture-specific code is not permitted to modify the errno variable.  drivers/ and libc/:  OS references to the errno variable should always use the set_errno(), get_errno() macros

net/route/net_fileroute.c

@@ -170,7 +170,7 @@ int net_routesize(FAR const char *path, size_t entrysize)
        * created yet?
        */
 
-      errcode = errno;
+      errcode = get_errno();
       if (errcode == ENOENT)
         {
           /* The routing table file has not been created.  Return size zero. */