Adding USD to a lite build fails to build due to boost errors, when you turn
boost on and rebuild still boost errors, boost was silently turned off since
it was not deemed needed. Once boost was forced on, it still fails due to TBB
being off.
This patch fixes:
- The Silent disabling of boost
- Add a check that USD is is not on before doing that
- move the TBB checks to a central location rather than the individual platform files
- Add USD to the TBB checks.
Differential Revision: https://developer.blender.org/D6479
Reviewers: brecht, sybren
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