CLB_MUXF8 Minitest

Purpose

This tests an issue related to Vivado 2017.2 vs 2017.3 changing MUXF8 behaviorThe general issue is the LUT6_2 cannot be used with a MUXF8 (even if O5 is unused)

General notes:

• 2017.2: LUT6_2 works with MUXF8
• 2017.3: LUT6_2 does not work with MUXF8
• All: LUT6 works with MUXF8
• All: MUXF8 (even with MUXF7) can be instantiated unconnected
• 2017.4 seems to behave like 2017.3