Fix #104, Short term build fix for implicit endian functions

[skliper]

Describe the contribution
Quick temporary fix for implicit declaration of endian functions on some systems (RH/CentOs). Note the real fix will be #95, custom implementation of these functions and removal of the messy defines.

Fix #104

Testing performed
Built cleanly on CentOS (confirmed build error before change and error gone after)

Expected behavior changes
No build errors on CentOS

System(s) tested on

• Hardware: Intel i5, WSL
• OS: CentOS 7.6.1810
• Versions: bundle w/ this change

Additional context
#95 is real fix, this is a quick fix to avoid build errors

Third party code
None

Contributor Info - All information REQUIRED for consideration of pull request
Jacob Hageman - NASA/GSFC

[jphickey]

Note that the original symbol _BSD_SOURCE_ (trailing underscore) was wrong, it is just _BSD_SOURCE. That might be why it didn't work.

Also glibc says you shouldn't directly set internal __USE_BSD symbol - this is computed by features.h based on _BSD_SOURCE.

Recommend to remove __USE_BSD and _BSD_SOURCE_. Or I suppose it can be just merged as-is if we are confident that this is just a short term thing.

[skliper]

Note that the original symbol _BSD_SOURCE_ (trailing underscore) was wrong, it is just _BSD_SOURCE. That might be why it didn't work.

Also glibc says you shouldn't directly set internal __USE_BSD symbol - this is computed by features.h based on _BSD_SOURCE.

Recommend to remove __USE_BSD and _BSD_SOURCE_. Or I suppose it can be just merged as-is if we are confident that this is just a short term thing.

Thanks for looking into it. I'll update and retest.

[skliper]

Retested on both Ubuntu and CentOS w/ no build errors

[jphickey]

Great, this is cleaner!