differentiate between 64 bit and 128 bit (R_SUBMMWHOLE) SSE vector regs,
and support spilling/assembling for R_SUBQ SSE registers (8 bytes)
(mantis #23962)
We currently never use the full 128 bit of an SSE register, and
spilling for those hasn't been implemented yet either (R_SUBMMWHOLE
SSE regs are spilled into a 4-byte temp currently -> can overwrite data)
git-svn-id: trunk@23700 -