Explicitly compile core.oat with the Quick compiler.

Change-Id: Id9e301268a75f6002855c690c9324bbcbee3ed6e
Fix Thumb2 assembler to emit 16-bit add/sub SP, #imm.

Also allow 16-bit add rN, SP, #imm.

Change-Id: I50100ad0b0e19a1c855a2319615e86d7a2b66a69
Merge "Explicitly compile core.oat with the Quick compiler."
Merge "Fix Thumb2 assembler to emit 16-bit add/sub SP, #imm."