Address `-Wnull-dereference' warnings from GCC 10.x.

Bump SONAME accordingly.

Fixes #298.

Change-Id: Ied9fd343a1627f49719c0ff0779503493124870e
Reviewed-on: https://code-review.googlesource.com/c/re2/+/58190
Reviewed-by: Paul Wankadia <junyer@google.com>
4 files changed