Install `re2.pc` with CMake too.

Fixes #399.

Change-Id: Ie84428f6d1039ac598ed3a3aa29395493a672ec5
Reviewed-on: https://code-review.googlesource.com/c/re2/+/60790
Reviewed-by: Paul Wankadia <junyer@google.com>
Reviewed-by: Perry Lorier <perryl@google.com>
3 files changed