Separate build/install for libre2.a and libre2.so.

This allows packaging to build/install one or the other rather than
both. Fedora already delete libre2.a and now Gentoo want to do this
cleanly.

Fixes #258.

Change-Id: Ie1e265b6d0ed72deecf3b154107f50970731a7fc
Reviewed-on: https://code-review.googlesource.com/c/re2/+/56475
Reviewed-by: Paul Wankadia <junyer@google.com>
1 file changed