Merging r348181:

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r348181 | lebedevri | 2018-12-03 12:07:58 -0800 (Mon, 03 Dec 2018) | 8 lines

[InstCombine] foldICmpWithLowBitMaskedVal(): disable 2 faulty folds.

These two folds are invalid for this non-constant pattern
when the mask ends up being all-ones:
https://rise4fun.com/Alive/9au
https://rise4fun.com/Alive/UcQM

Fixes https://bugs.llvm.org/show_bug.cgi?id=39861
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llvm-svn: 348528