curl: add missing type sizes for 'long long' and '__int64'

When generating curl_config.h, add size information for long long and __int64 types. These are needed as candidates for defining the ssize_t type because on MSVC, long is not the same size as size_t.

This problem did not affect upstream curl because it computes the ssize_t type in CMake code where all sizes are available. CMake's port computes it in preprocessor logic because universal binaries on macOS do not know type sizes until compile time.

Fixes: #18477