* add x86 encodings for shift-immediate instructions
implements encodings for ishl_imm, sshr_imm, and ushr_imm. uses 8-bit immediates.
added tests for the encodings to intel/binary64.cton. Canonical versions
come from llvm-mc.
* translate test to use shift-immediates
* shift immediate encodings: use enc_i32_i64
and note why the regular shift encodings cant use it above
* add additional encoding tests for shift immediates
this covers 32 bit mode, and 64 bit operations in 64 bit mode.
This enables code generation that never causes a SIGFPE signal to be
raised from a division instruction. Instead, division and remainder
calculations are protected by explicit traps.
