Address gethostname failure due to missing WinSock initialization

[eramongodb]

Addresses the following stderr output by the test_bson test binary on Windows:

unable to get hostname: 0

This message is emitted by a call to gethostname in _bson_context_get_hostname by the following stack trace:

bsoncxx::v_noabi::oid::oid()
  - bson_oid_init(bson_oid_t *oid, bson_context_t *context)
  - bson_context_get_default()
  - _bson_context_init_default()
  - _bson_context_init(bson_context_t *context, bson_context_flags_t flags)
  - _bson_context_init_random (bson_context_t *context, bool init_seq)
  - _bson_context_get_hostname (char out[HOST_NAME_MAX])
  - gethostname (char *name, int namelen)

Patching the mongoc library to print the value of WSAGetLastError (rather than errno) reveals an error code value of WSANOTINITIALIZED. This reveals that gethostname, a function provided by the WinSock library, is being invoked before a successful call to WSAStartup. This call is usually handled by mongoc_init. However, test_bson does not use the mongoc or mongocxx library. Therefore, it does not call mongoc_init or WSAStartup before calling bson_oid_init.

This PR proposes a straightforward workaround to manually invoke WSAStartup prior to executing the test suite on Windows. Filed CDRIVER-5957 to investigate a more thorough solution to this problem (e.g. document that mongoc_init or WSAStartup must have been invoked first? add internal calls to WSAStartup/WSACleanup that wrap the gethostname on Windows?).

[kevinAlbs]

LGTM. Nice investigation.

Filed CDRIVER-5957

Commented with idea for alternative.