Fix our variable naming in the CMake build. CMake's pkg-config finder sets BROTLI_INCLUDE_DIR when searching for the Brotli libraries. * CMakeLists.txt, build/FindBrotli.cmake: Use BROTLI_INCLUDE_DIR instead of BROTLI_INCLUDES. git-svn-id: https://svn.apache.org/repos/asf/serf/trunk@1930991 13f79535-47bb-0310-9956-ffa450edef68