Write C/CXX Flags into CMake Cache

While passing the CMake Toolchain to external dependencies
like CAPU, the C/CXX Flags get lost in case they are not in the CMake cache.

git-svn-id: https://svn.apache.org/repos/asf/etch/trunk@1679946 13f79535-47bb-0310-9956-ffa450edef68