Implement strerror, errno. Fixes #728

[kamphaus]

Fixes #728

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This change is 

[codecov]

Codecov Report

Merging #729 into master will decrease coverage by 0.14%.
The diff coverage is 45.65%.

@@            Coverage Diff             @@
##           master     #729      +/-   ##
==========================================
- Coverage   81.63%   81.48%   -0.15%     
==========================================
  Files         165      166       +1     
  Lines        9214     9259      +45     
==========================================
+ Hits         7522     7545      +23     
- Misses       1281     1301      +20     
- Partials      411      413       +2

Impacted Files	Coverage Δ
program/function_definition.go	100% <ø> (ø)	⬆️
noarch/util.go	70.21% <0%> (-18.98%)	⬇️
noarch/stdio.go	83.4% <36.36%> (-1.05%)	⬇️
noarch/errno.go	68% <68%> (ø)

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[elliotchance]

Reviewed 2 of 5 files at r2, 3 of 3 files at r3.
Review status: all files reviewed at latest revision, all discussions resolved.

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