Add endian detection for OS X, Windows and *BSD

[lovell]

Hello, this PR builds on the work started in commit c56aabf by adding endian detection support for Windows, OS X and *BSD variants as well as the already-supported Linux.

CI test results with this change:

• Linux
• OS X
• Windows

The current master branch fails to compile on these platforms without the proposed changes.

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[lovell]

I signed it!

[googlebot]

CLAs look good, thanks!

[lovell]

Thank you for merging.

[geoffpike]

Thank you for contributing!​