Stack management: tcb->adj_stack_size should be without tls overhead

[johannes-nivus]

Since there are external tools (e.g. debugger with task/stack awareness) that use tcb->adj_stack_size for stack overflow checking by means of stack coloration, they continously report stack overflows because they interpret tls as used stack.
Also from a logical point of view: stack_size should be stack size.
#1562 fixes this for arm architecture. This should be fixed for other architectures as well.