This commit does four things:
* Adds "pb.ss" and "pb.c", which implement a portable bytecode
backend and interpreter that is intended for bootstrapping. A
single set of pb bootfiles can support bootstrapping on all
platforms --- as long as the C compiler supports a 64-bit integer
type. The pb machine supports foreign calls for only a small set of
recognized prototypes, and it does not support foriegn callables.
Use `./configure --pb` to build the pb variant.
* Changes the kernel's casts between `ptr` and `void*` types. In a pb
build, the `ptr` type can be a 64-bit integer type while `void*` is
a 32-bit pointer type, so casts must go through an intermediate
integer type.
* Adjusts the compiler to accomodate run-time-determined endianness.
Making the compiler agnostic to word size is not practical, but
only a few pieces depend on the target machine's endianness, and
those can generally be deferred to a run-time choice of byte-based
operations. The one exception is that ftype bit fields are not
allowed unless accompanied by an explicit endianness declaration.
* Start reducing duplication among platform-specific makefiles. For
example, `Mf-ta6osx` chains to `Mf-a6osx` to avoid repeating most
of it. A lot more can be done here.
original commit: 97533fa9d8b8400b0dc1a890768c7d30c91257e0
f78dc5724e