1.1.10: will be tagged as "sbcl-1.1.10"
Microoptimize type-tests on x86oids.

On x86-64 in %test-lowtag instead of doing:

MOV EAX, ECX
AND AL, 15
CMP AL, 15
do
LEA EAX, [RCX-15]
TEST AL, 15

Which allows to save one byte.

On x86 this optimization is already applied, but since LEA loads a
32-bit integer, EAX can be later used as an already untagged pointer
in %test-headers: MOV EAX, [ECX-7] => MOV EAX, [EAX], which takes one
byte less to encode.
Optimize (unsigned-byte 32/64) type tests on x86oids.

Instead of doing
TEST CL, 3
MOV EAX, ECX

do
MOV EAX, ECX
TEST AL, 3

AL has shorter encoding and can save 1 byte with ECX or 4 bytes with
ESI, which doesn't have SIL on x86.

Also revert a part of the previous commit which used untagged
pointers, which can cause problems with the GC.