[libc][math] Improve the performance and error printing of UInt.

Use add_with_carry builtin to improve the performance of
addition and multiplication of UInt class.  For 128-bit, it is as
fast as using __uint128_t.

Microbenchmark for addition:
https://quick-bench.com/q/-5a6xM4T8rIXBhqMTtLE-DD2h8w

Microbenchmark for multiplication:
https://quick-bench.com/q/P2muLAzJ_W-VqWCuxEJ0CU0bLDg

Microbenchmark for shift right:
https://quick-bench.com/q/N-jkKXaVsGQ4AAv3k8VpsVkua5Y

Microbenchmark for shift left:
https://quick-bench.com/q/5-RzwF8UdslC-zuhNajXtXdzLRM

Reviewed By: sivachandra

Differential Revision: https://reviews.llvm.org/D137871