Fix handling of do_pending_interrupt on ARM.

sigtrap_handler didn't recognize the interrupt done by
do_pending_interrupt as being a pending interrupt.
It was looking for SWILT, but it used SWIAL, but since SWIAL isn't
used for error breaks anymore, just make sure that it's a SWI instruction.

Reported by Jerry James.
Some reader cleanups.

- Fewer special-variable references, slightly smaller/faster.

- Remove spurious double assignment of dispatch macros.

- Tokens returned from READ-EXTENDED-TOKEN[-ESCAPED] have not
  undergone case-conversion. The only place where it matters
  is for the #: reader, which calls CASIFY-READ-BUFFER.

- #\ and #* readers don't copy the read buffer.
Consistently pass a readtable to the character attribute testers.

This is marginally better for semantics and maybe performance.
Tweak %INSTANCE-TYPEP deftransform a little more:

 - There remained some cases that used the general LAYOUT-OF function
   which had to look in **BUILT-IN-CLASS-CODES** even though every
   layout in that array would ultimately fail the subsequent tests.
   Now all paths through the transform emit code which immediately
   fails objects that are neither instance nor funcallable-instance.

 - Flip the order of the hierarchy-based test and the layout-EQ test
   if it looks like the EQ test could never pass. But check it always.

 - Except not for SEQUENCE because no object's layout can ever be
   EQ to #<LAYOUT for SEQUENCE>.  Just use the hierarchy.
x86-64: Allow constant TNs for CMOV. Also unbreak "chill"
Pedantically replace many uses of :EOF, NIL, and *EOF-OBJECT* with +EOF+.

Unlike in C where the eof value is (supposedly) opaque,
it is silly to provide an EOFP predicate because you still wonder
which particular eof-value it refers to.  *EOF-OBJECT* is not
as obvious as (EQ x +EOF+), and in contrast to LOAD, nothing about
token-level input demands an unforgeable object, so just use 0.
Update some internal notes