Rather than re-invent endian defines, as well as maintain our own list
of OS & arch-specific includes, punt all that logic in favor of the bfd
ones already set up and maintained elsewhere. We already rely on the
bfd library, so leveraging the endian aspect should be fine.
This was done for all the other ports years ago, so catch ppc up.
The --enable-sim-hostendian flag was purely so people had an escape route
for when cross-compiling. This is because historically, AC_C_BIGENDIAN
did not work in those cases. That was fixed a while ago though, so we can
require that macro everywhere now and simplify a good bit of code.
This was done for all the other ports years ago, so catch ppc up.
The defs.h header will take care of including the various config.h
headers. For now, it's just config.h, but we'll add more when we
integrate gnulib in.
This header should be used instead of config.h, and should be the
first include in every .c file. We won't rely on the old behavior
where we expected files to include the port's sim-main.h which then
includes the common sim-basics.h which then includes config.h. We
have a ton of code that includes things before sim-main.h, and it
sometimes needs to be that way. Creating a dedicated header avoids
the ordering mess and implicit inclusion that shows up otherwise.
