Fix compilation of embedded libjson for VS2012 / MSVC_VER 1700 (#5238, trunk only, @FOSS4G2013)

git-svn-id: https://svn.osgeo.org/gdal/trunk@26484 f0d54148-0727-0410-94bb-9a71ac55c965
Merge branch 'trunk' into trunk_mingw