Move CMAKE_USE_OPENSSL and CURL_CA_BUNDLE up to the top of CMake so that
CMake's own sources can know their values. Add the CURL_CA_PATH option
at the top and honor it as part of the curl build.
Re-apply the logic change made by commit v2.8.2~536 (Use arch-aware
CHECK_TYPE_SIZE result, 2009-12-17). The size of some types must be
selected at preprocessing time when building for multiple archs on OS X.
Brad King