[PATCH 0/4] more clang/sanitizer fixes

Here are some more sanitizer fixes, this time from trying with clang-11. These should go on top of jk/asan-build-fix if you want to get a successful run with "make CC=clang-11 SANITIZE=address,undefined test".

I don't think any of them is indicative of a current bug in practice, but the UBSan stuff makes me worried that an aggressive compiler might do the wrong thing in some case.

  [1/4]: merge-recursive: silence -Wxor-used-as-pow warning
  [2/4]: avoid computing zero offsets from NULL pointer
  [3/4]: xdiff: avoid computing non-zero offset from NULL pointer
  [4/4]: obstack: avoid computing offsets from NULL pointer

 compat/obstack.h  |  6 ++++--
 merge-recursive.c | 19 ++++++++++++++-----
 sequencer.c       |  6 +++---
 unpack-trees.c    |  2 +-
 xdiff-interface.c | 12 ++++++++----
 5 files changed, 30 insertions(+), 15 deletions(-)

-Peff