clang-format: Improve binary operator detection.

Before:
  *(int *)(p &~3UL) = 0;

After:
  *(int *)(p & ~3UL) = 0;

This fixes llvm.org/PR19464.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@207405 91177308-0d34-0410-b5e6-96231b3b80d8