[ARM] Use ADDCARRY / SUBCARRY

This is a preparatory step for D34515 and also is being recommitted as its
first version caused PR34045.

This change:
 - makes nodes ISD::ADDCARRY and ISD::SUBCARRY legal for i32
 - lowering is done by first converting the boolean value into the carry flag
   using (_, C) ← (ARMISD::ADDC R, -1) and converted back to an integer value
   using (R, _) ← (ARMISD::ADDE 0, 0, C). An ARMISD::ADDE between the two
   operations does the actual addition.
 - for subtraction, given that ISD::SUBCARRY second result is actually a
   borrow, we need to invert the value of the second operand and result before
   and after using ARMISD::SUBE. We need to invert the carry result of
   ARMISD::SUBE to preserve the semantics.
 - given that the generic combiner may lower ISD::ADDCARRY and
   ISD::SUBCARRYinto ISD::UADDO and ISD::USUBO we need to update their lowering
   as well otherwise i64 operations now would require branches. This implies
   updating the corresponding test for unsigned.
 - add new combiner to remove the redundant conversions from/to carry flags
   to/from boolean values (ARMISD::ADDC (ARMISD::ADDE 0, 0, C), -1) → C
 - fixes PR34045

Differential Revision: https://reviews.llvm.org/D35192

llvm-svn: 313009