Small correction, using the hello_mongoc project, when following the link above, i do of course not get missing __img_bson_free (that would mean the bson lib as such is missing), but i get these:
1>bson-static-1.0.lib(bson.obj) : error LNK2019: unresolved external symbol __imp_strspn referenced in function should_ignore
1>bson-static-1.0.lib(bson.obj) : error LNK2019: unresolved external symbol __imp__time64 referenced in function time
1>bson-static-1.0.lib(bson-oid.obj) : error LNK2001: unresolved external symbol __imp__time64
1>bson-static-1.0.lib(bson-decimal128.obj) : error LNK2019: unresolved external symbol __imp_isupper referenced in function _dec128_tolower
1>bson-static-1.0.lib(bson-string.obj) : error LNK2001: unresolved external symbol __imp_isupper
1>bson-static-1.0.lib(bson-decimal128.obj) : error LNK2019: unresolved external symbol __imp_isdigit referenced in function bson_decimal128_from_string_w_len
1>bson-static-1.0.lib(bson-string.obj) : error LNK2001: unresolved external symbol __imp_isdigit
1>bson-static-1.0.lib(bson-iso8601.obj) : error LNK2001: unresolved external symbol __imp_isdigit
1>bson-static-1.0.lib(bson-decimal128.obj) : error LNK2019: unresolved external symbol __imp___stdio_common_vsscanf referenced in function _vsscanf_s_l
1>bson-static-1.0.lib(bson-error.obj) : error LNK2019: unresolved external symbol __imp_strerror_s referenced in function bson_strerror_r
1>bson-static-1.0.lib(bson-string.obj) : error LNK2019: unresolved external symbol __imp_isalpha referenced in function bson_ascii_strtoll
1>bson-static-1.0.lib(bson-string.obj) : error LNK2019: unresolved external symbol __imp_isspace referenced in function bson_isspace
1>bson-static-1.0.lib(bson-string.obj) : error LNK2019: unresolved external symbol __imp__stricmp referenced in function bson_strcasecmp
1>bson-static-1.0.lib(bson-iso8601.obj) : error LNK2019: unresolved external symbol __imp__gmtime64_s referenced in function gmtime_s
1>bson-static-1.0.lib(bson-iso8601.obj) : error LNK2019: unresolved external symbol __imp_strftime referenced in function _bson_iso8601_date_format
1>C:\repos\mongo-cxx-driver-r4.0.0\build\_deps\mongo-c-driver-build\src\libmongoc\Debug\hello_mongoc.exe : fatal error LNK1120: 11 unresolved externals