Disable abi diffs for sanitized variants of modules.

asan variants can sometimes have extra exported symbols (this is a vndk
extension violation). Since asan variants are only used for testing,
don't do abi diffs for them.

Bug: 66301104

Test: Without the change, libc++.so.lsdump exists for the asan variant;
      with the change, it does not.

Test: make -j64.

Change-Id: I61a4c7a3e9aa0028a54ad0ca8715e8c77aebad94