Implement XOR / SHR / SHL on amd64 native backend.

[twitchyliquid64]

As before, relies on previous PRs.

[codecov-io]

Codecov Report

Merging #117 into master will decrease coverage by 0.04%. The diff coverage is 57.14%.

@@            Coverage Diff             @@
##           master     #117      +/-   ##
==========================================
- Coverage   65.65%   65.61%   -0.05%     
==========================================
  Files          41       41              
  Lines        3916     3949      +33     
==========================================
+ Hits         2571     2591      +20     
- Misses       1078     1091      +13     
  Partials      267      267

Impacted Files	Coverage Δ
exec/internal/compile/scanner.go	0% <0%> (ø)	:arrow_up:
exec/internal/compile/backend_amd64.go	78.62% <66.66%> (-1.21%)	:arrow_down:

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[twitchyliquid64]

:airplane: :)