Remove some duplication in the handling of __attribute__((ext_vector_size(N))).


git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@172340 91177308-0d34-0410-b5e6-96231b3b80d8
Added builtins for multiprecision adds.

We lower all of these intrinsics into a 2x chained usage of
uadd.with.overflow.

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@172341 91177308-0d34-0410-b5e6-96231b3b80d8