[llvm] r267111 - [EarlyCSE] Take the intersection of flags on instructions

Hi David,

When I reverted r267098 in r267127, one of the EarlyCSE tests failed on a couple builders (http://lab.llvm.org:8011/builders/llvm-hexagon-elf/builds/28174, http://lab.llvm.org:8011/builders/llvm-clang-lld-x86_64-scei-ps4-ubuntu-fast/builds/11173). Going by the logs it was CSE'ing two adds where one had the nuw flag and one didn't. The failures disappeared by themselves in the next build but I thought I should mention it anyway.