x86_64: Fix neg_double

In a case, when src and dest regs are the same, previous
implementation of the neg_double bytecode returns an
incorrect result.

This implementation uses shifts and xor and works for both
cases.

Change-Id: I137d9a90298ec225d80435d35558da8abb69cd01
Signed-off-by: Alexei Zavjalov <alexei.zavjalov@intel.com>
4 files changed