Change-Id: I6503b73978c9b2f4693422b62a74d4e1c75409c7
Reviewed-on: https://code-review.googlesource.com/c/re2/+/44491
Reviewed-by: Paul Wankadia <junyer@google.com>

There are two changes in this patch but they are related because they
both improve install target generated by CMake.

1) GNUInstallDirs is now used to determine name of the folders where
libraries and headers are installed. On RedHat based Linux
distributions, usual folder for x86-64 libraries is lib64 and not just
simply lib. GNUInstallDirs takes care of deciding which name to use.

2) Pkgconfig file was not installed when CMake was used. Adding pc file
to the installation process of CMake install target allows package
maintainers to easily provide packages which work both with pkgconfig
and CMake.

Fixes #215.

Change-Id: Icc9636039e5456df78323b7ae1b89e0d27be7fbf
Reviewed-on: https://code-review.googlesource.com/c/re2/+/43990
Reviewed-by: Paul Wankadia <junyer@google.com>

Change-Id: Ib7867190116fbc65d404804c4f14392f599d8bd3
Reviewed-on: https://code-review.googlesource.com/c/re2/+/44510
Reviewed-by: Paul Wankadia <junyer@google.com>

If CMake doesn't support building libre2.a and libre2.so together and
installing them together, then it isn't suitable for use in packaging
and so installing re2.pc isn't needed.

Fixes #215.

Change-Id: I83e329f39da97ed6c4184564bd4ac85709800213
Reviewed-on: https://code-review.googlesource.com/c/re2/+/44630
Reviewed-by: Paul Wankadia <junyer@google.com>