I get redclaration error(found by resharper for c++) in visual studio 2013:
28c4aa26-7fc6-11e6-8454-8b7cece4aeb2.png
vs2013 have partial support of come c99 standard so looks like size_t is already defined in crtdefs.h
Here is fix: https://github.com/mongodb/libbson/pull/178/files