1.0.25.3: earlier x86 code-object fixup envectorization

1.0.25.3: earlier x86 code-object fixup envectorization

In order to be able to relocate code-objects, the x86 port has to keep
track of the locations of certain fixups within the objects (these
fixups being relative fixups pointing to addresses outside the
code-object and absolute fixups pointing to addresses within the
code-object).  Since time immemorial, the build process involved having
genesis dump a record of each fixup to be recorded as a cold-toplevel,
and cold-init passing such cold-toplevel information to
!envector-load-time-code-fixup.

  * Change genesis to create fixup-vectors directly, instead of dumping
    the fixup information as cold-toplevels.

  * Strip out the (now dead) code for envectoring cold-toplevels during
    cold-init.