Update x/sys to support go 1.17

[gordonbondon]

Updating x/sys so that this project supports go 1.17.

More context: Homebrew/homebrew-core#83413

Without this fix running a binary can cause a panic, see upstream go issue: golang/go#45702

Please cut a release after this is merged.

[codecov]

Codecov Report

Merging #100 (8d2a997) into master (fea0fbd) will increase coverage by 0.66%.
The diff coverage is n/a.

❗ Current head 8d2a997 differs from pull request most recent head 24300fc. Consider uploading reports for the commit 24300fc to get more accurate results

@@            Coverage Diff             @@
##           master     #100      +/-   ##
==========================================
+ Coverage   75.72%   76.39%   +0.66%     
==========================================
  Files          40       40              
  Lines        4318     3385     -933     
==========================================
- Hits         3270     2586     -684     
+ Misses        854      605     -249     
  Partials      194      194              

Impacted Files	Coverage Δ
middleware/middleware.go	79.16% <0.00%> (-2.86%)	⬇️
dnsutil/dnsutil.go	80.92% <0.00%> (-1.38%)	⬇️
middleware/response_writer.go	90.47% <0.00%> (-1.20%)	⬇️
middleware/hostsfile/hostsfile.go	84.46% <0.00%> (-1.14%)	⬇️
authcache/authserver.go	95.00% <0.00%> (-1.00%)	⬇️
server/server.go	97.29% <0.00%> (-0.67%)	⬇️
middleware/metrics/metrics.go	96.87% <0.00%> (-0.57%)	⬇️
middleware/edns/edns.go	87.69% <0.00%> (-0.55%)	⬇️
authcache/ns_cache.go	85.18% <0.00%> (-0.53%)	⬇️
mock/writer.go	92.68% <0.00%> (-0.50%)	⬇️
... and 30 more

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