[X86] Add test cases to show where LowerSELECT doesn't select SADDO/SSUBO to INC...

[X86] Add test cases to show where LowerSELECT doesn't select SADDO/SSUBO to INC/DEC, but LowerXALUOOp does. Leading to duplicate code.

When SADDO/SSUBO is used as a part of a condition, the X86 backend has to lower the instruction twice. One for the flags use and then once for the data use. These two selections should be kept in sync so they end up with one node providing the data and the flags. This doesn't seem to be happening for INC/DEC.

llvm-svn: 350194