First pass at some exception stuff

Stubs for entry and exit from exception are in place. Entry seems to
work in the simple case, though exit is untested.

Also fix vectors to identify _hang as thumb function so that the T bit
is set correctly.
Indicate stalls explicitly in decompile mode
Add add family of decompiles, adc_reg_t2
Add some decompiles, revise how <IT> is handled
Finish adding decompile entries
decompile: handle IT block cases better
Add decompile check; fix decompile itstate
Use full names through function (fixes unused 'U')
Switch object files from built-in to unified group
Add a variant that builds with optimization at max
Convert apsr,ipsr,epsr access to export_inline
convert primask,faultmask,basepri to export_inline
Add NDEBUG to fast variant, fix bad assertions

Many assertions had code that required execution in them, e.g.
    asssert(1 = recv(...));
which breaks in the face of NDEBUG when assert goes away. Switch these
over to the better practice of if's and explicit errrors.
Switch state_read to export_inline
Convert CORE_reg_read to export_inline
Include cycle count in timing warning
Add an optimized nopipeline variant

Getting at reasonable performance with this configuration, some
oversimplified tests get this up to ~835 khz average speed running fib
on my 2.7 ghz macbook core i7 (that was otherwise lightly loaded).