Don't try to emit nullability fix-its within/around macros.

The newly-added notes from r290132 are too noisy even when the fix-it
is valid. For the existing warning from r286521, it's probably the
right decision 95% of the time to put the change outside the macro if
the array is outside the macro and inside otherwise, but I don't want
to overthink it right now.

Caught by the ASan bot!

More rdar://problem/29524992

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@290141 91177308-0d34-0410-b5e6-96231b3b80d8