Add string.Memcmp

[rjalfa]

Added memcmp and corresponding integration test.

[Konstantin8105]

As I understood, also need registrate function here:

c4go/program/function_definition.go

Line 207 in 7b105cf

"string.h": {

[codecov-io]

Codecov Report

Merging #155 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #155      +/-   ##
==========================================
+ Coverage   88.04%   88.05%   +<.01%     
==========================================
  Files         168      168              
  Lines        9419     9426       +7     
==========================================
+ Hits         8293     8300       +7     
  Misses        773      773              
  Partials      353      353

Impacted Files	Coverage Δ
program/function_definition.go	91.86% <ø> (ø)	⬆️
noarch/string.go	100% <100%> (ø)	⬆️

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[Konstantin8105]

Thank you for PR.