adjust the walker's handling of variables a little bit

The walker notes information about variable bindings (and symbol
macros) in the env-lock, but didn't look in the lexenv itself if
the env-lock lookup failed.  This had a bunch of consequences,
notably lp#1368305 and similar.

While we're at it, make the walker aware of global symbol macros
as well (lp#375326)
Remove (deftype sap-int () '(unsigned-byte 32/64)) on x86oids.

It's not used anywhere and is only defined on x86oids.
Fix issue with new GC fixes choking on padding, reported on x86 (32
bits).  Put useful error message for the next time a similar issue
comes up.

Fix cracauer-only indentation.
Fix non-x86/precise-gc build.