The output path for this file was left incorrect in the previous PR for PHPC-1174, but the file isn't actually even used anymore per mongodb/mongo-c-driver@abc882dec9 (CDRIVER-2473).
The check for sasl_client_done was inadvertently removed by aab92e1d3e. This ensures that we check for the symbol regardless of whether SASL was found with pgk-config or PHP_CHECK_LIBRARY.
libmongoc does not actually support GSSAPI (CDRIVER-2170), so we should not allow building with it. This also reverts preference for the GSS framework on macOS (PHPC-1142).
GitHub's file finder filters out "build/" directories, among others, which can make it difficult to quickly access these files. Also, the "build/" directory doesn't provide much value here, since it only contains "autotools/".
