Unary Not (boolean and bitwise) is no longer a separate LLVM instruction

but is instead implemented with XOR.  Note that the InstrForest opLabels
for Not and BNot remain the same, i.e., the XOR is recognized and
represented as a (boolean or bitwise) Not when building the instruction
trees.  But these tree nodes are now binary, not unary.

llvm-svn: 3343