jsoncpp: Fix vs7 build error from missing C99 functions

See pull request #46 upstream:
https://github.com/open-source-parsers/jsoncpp/pull/46

Change-Id: I8eb655114d0a9d17ec9124108a699fb97870c43c
Merge topic 'fix-jsoncpp-on-vs7' into master

6b4f8cbb jsoncpp: Fix vs7 build error from missing C99 functions