This feature was controlled by the compilation flag `OPDISP`
which would enable some bits of assembler on the x86 (ISC or DOS)
or some other specialized code on SPARC. On SPARC hardware, there
was a special compilation process that would preprocess the code
and generate dispatch tables.
We do this now when this feature is enabled using gcc's computed
gotos feature. This is available in clang and some other compilers.
Notably, it isn't present in Visual Studio.
This doesn't decrease our portability at all as this feature is
optional and it replaces specialized assembler code with C using
compiler extensions (making it cross-platform).
In doing this, we've removed a bunch of related code, however,
it is likely that other pieces yet remain and will be removed
in subsequent commits as we clean things up and refine them.
This feature remains disabled by default for now.
* Use gcc / clang overflow builtins.
This avoids expensive checks for overflow that employ undefined
behavior.
This is a step along the way towards replacing the old hand-written
assembler that did the same thing in terms of using the CPU's
overflow detection.
* Remove unimplemented SPARC asm for multiplication, divide, and remainder.
This wasn't implemented before, and for multiplication, it is now
implemented for gcc and friends using overflow detection.
* Remove USE_INLINE_ARITH.
Now that we have the compiler built-ins for detecting overflow,
we don't need custom assembly for it for each platform.
For now, we keep, but still don't use, the code that do a hot
path through the dispatch loop for some math. This code isn't
actually running or in use, but it is separate from how the
other inline arithmetic was being performed. These are the
`fast_op_*` functions that are implemented in assembler.
* Delete code related to NATIVETRAN feature.
This was obsolete work that had been done for generating
native code from the bytecode.
ClosesInterlisp/medley#89.
* Remove unused SaveD6.
