[clang][dataflow] #llvm #flow-analysis Simplify formula at CNF construction...

[clang][dataflow] #llvm #flow-analysis Simplify formula at CNF construction time, and short-cut solving of known contradictory formulas.

In dataflow analysis, SAT solver: simplify formula during CNF construction and short-cut
solving when the formula has been recognized as contradictory.

Reviewed By: sammccall

Differential Revision: https://reviews.llvm.org/D158407