[fix] failed to compile on FreeBSD

[TingDaoK]

Issue #, if available:

• Compilation of v0.10.3 broken on FreeBSD #523

Description of changes:

• Move the platform specific code to aws-c-io and update the code to use that.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 67.64706% with 11 lines in your changes missing coverage. Please review.

Project coverage is 79.56%. Comparing base (bfa0392) to head (ef24170).

Files with missing lines	Patch %	Lines
source/no_proxy.c	67.64%	11 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #527      +/-   ##
==========================================
- Coverage   79.73%   79.56%   -0.18%     
==========================================
  Files          28       28              
  Lines       11811    11833      +22     
==========================================
- Hits         9418     9415       -3     
- Misses       2393     2418      +25     

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