target/i386: move C0-FF opcodes to new decoder (except for x87)

target/i386: move C0-FF opcodes to new decoder (except for x87)

The shift instructions are rewritten instead of reusing code from the old
decoder.  Rotates use CC_OP_ADCOX more extensively and generally rely
more on the optimizer, so that the code generators are shared between
the immediate-count and variable-count cases.

In particular, this makes gen_RCL and gen_RCR pretty efficient for the
count == 1 case, which becomes (apart from a few extra movs) something like:

  (compute_cc_all if needed)
  // save old value for OF calculation
  mov     cc_src2, T0
  // the bulk of RCL is just this!
  deposit T0, cc_src, T0, 1, TARGET_LONG_BITS - 1
  // compute carry
  shr     cc_dst, cc_src2, length - 1
  and     cc_dst, cc_dst, 1
  // compute overflow
  xor     cc_src2, cc_src2, T0
  extract cc_src2, cc_src2, length - 1, 1

32-bit MUL and IMUL are also slightly more efficient on 64-bit hosts.

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>