1.0.41.21: runtime: Current stack and frame pointers are per-thread data.

1.0.41.21: runtime: Current stack and frame pointers are per-thread data.

  * Add slots to the thread structure on threaded targets to hold
the control stack and frame pointers.

  * Add some macros to thread.h to grab the correct variable or
slot on all builds, and use them everywhere required.

  * Conditional-compile out the old global variables for this on
threaded targets (I probably messed this up).