This reduces dependency on assembler, and allows to consolidate global
variables in the future.

Addresses issue #1022.

These changes were tested with QEMU, and by few people of real hardware.

Blanket wide to all .c and .h files.  Some files originating from ST are
difficult to deal with (license wise) so it was left out of those.

Also merged modpyb.h, modos.h, modstm.h and modtime.h in stmhal/.

Specifically, nlr.h does.

And this is not good.

Having an optimized asm implementation is good, but if we want portability,
that's it.

If no nlr_buf has been pushed, and an nlr_jump is called, then control
is transferred to nlr_jump_fail (which should bail out with a fatal
error).

This does not affect code size or performance when debugging turned off.

To address issue #420.