move sdk files into arch subfolders

[tlambert03]

@jaimergp ... this look ok?

[codecov]

Codecov Report

Merging #29 (7969af0) into main (1e2d45b) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main      #29   +/-   ##
=======================================
  Coverage   87.29%   87.29%           
=======================================
  Files          11       11           
  Lines        1149     1149           
=======================================
  Hits         1003     1003           
  Misses        146      146           

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 1e2d45b...7969af0. Read the comment docs.

[jaimergp]

I'd rename Windows/AMD64 to Windows/x86_64 for consistency.