Use proper target dependencies for APR and APR-Util, and support
linking with static APR on Windows.

* build/FindAPR.cmake: Define targets APR::APR and APR::APR_static.
* build/FindAPRUtil.cmake: Define targets APR::APRUTIL and APR::APRUTIL_static.

* CMakeLists.txt:
  - Use the new APR::* target dependencies instead of variables,
    except for generating the pkg-config file.
  - Support the APR_STATIC flag on Windows.


git-svn-id: https://svn.apache.org/repos/asf/serf/trunk@1841780 13f79535-47bb-0310-9956-ffa450edef68
3 files changed